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谨以此纪念杰克
In Memory of Jack
介绍
Introduction
你是否“迷上了电子产品”，却在决定动手制作、排除故障或修理东西时，一看到那些晦涩难懂的符号图表就望而却步？如果是这样，那么你现在就拥有了解决方案。
Have you “caught the electronics bug” and then balked at the sight of diagrams with arcane symbols when you decided to build, troubleshoot, or repair something? If so, you have the solution in your hands.
遇到看起来很奇怪的电路图，不要放弃电子学。你不会因为害怕训练的艰苦就放弃你最喜欢的运动吧？当然不会！练习才能让你达到最佳状态。绘制合理、布局清晰的电路图（或称“原理图”）可以帮助你设计、制造、维护和修理电子设备。但是，你必须付出一些努力才能掌握阅读和理解电路图的技能。
Don’t give up on electronics when you encounter strange-looking circuit diagrams. You don’t quit your favorite sport because you fear the rigors of training, do you? No! You get into condition with practice. Schematic diagrams (or “schematics”), sensibly drawn and neatly arranged, can help you design, build, maintain, and repair electronic equipment. But you must do some work to gain skill at reading and interpreting schematics.
就像开车旅行一样，公路地图会指引你如何在乡间穿行。同样，在使用电子设备时，电路图会帮助你理解简单的电路、复杂的设备和庞大的系统。一旦你了解了这些符号的含义，就会发现电路图并不比公路地图更难懂。
As you plan a trip by car, road maps show you how to navigate the countryside. As you work with electronic equipment, schematics show you the way through simple circuits, complex devices, and massive systems. Once you know what the symbols represent, you’ll find schematics no more difficult than road maps.
阅读本书，你将了解电路图的基本原理，学习如何绘制和解读每个符号，以及这些符号如何相互连接形成功能电路。你还将有机会进行一些简单的实验。之后，你可以继续探索电子学的任何领域，从业余无线电到太空通信，从环绕声到虚拟现实。
While you read this book, you’ll learn the rationale of schematics, how to draw or interpret each symbol, and how the symbols interconnect to form functional circuits. You’ll also get a chance to do a few simple experiments. Then you can continue your quest in any field of electronics from amateur radio to space communications, from surround sound to virtual reality.
我的网站是www.sciencewriter.net。我也制作视频；只需在 YouTube 上搜索我的名字即可。祝您观看愉快！
You’ll find my website at www.sciencewriter.net. I also create videos; simply search YouTube for my name. Have fun!
斯坦·吉比里斯科
Stan Gibilisco
1
1
总体规划
The Master Plan
在电气和电子学文献中，您会遇到三种类型的图表。每种图表都有其独特的用途。购买电气或电子设备或系统时，理想情况下，它应该附带一份操作和维护手册，其中包含所有这三种类型的图表。
You’ll encounter three types of diagrams in electricity and electronics literature. Each style serves a unique purpose. When you buy an electric or electronic device or system, it should (in the ideal case) come with an operating and maintenance manual that includes all three types of diagrams.
框图可以帮助您了解系统中各个电路如何协同工作。每个电路都用一个“方框”（矩形或其他形状，具体取决于应用）表示。连接线（有时一端或两端带有箭头）显示了各个电路如何组合成整个系统，以及电流和信号如何在这些电路之间流动。图1-1是一个简单的示例。
• A block diagram gives you an overview of how the individual circuits in a system work together. You’ll see each circuit represented as a “block” (rectangle or other shape, depending on the application). Interconnecting lines, sometimes with arrows on one or both ends, show how the circuits combine to form the whole system, and how currents and signals flow among those circuits. Figure 1-1 is a simple example.
图 1-1 可发送摩尔斯电码信号的无线电发射机的框图。
FIG. 1-1 Block diagram of a radio transmitter that can send signals in Morse code.
电路原理图（通常简称为原理图）展示了电路中的每个元件。每个元件都有其特定的符号。元件之间的连线表示它们如何连接在一起，以及如何连接到电源，从而实现特定的功能或操作。本书主要讲解原理图。图 1-2是一个简单的示例。
• A schematic diagram (often simply called a schematic) shows every component in a circuit. Each component has its own special symbol. Lines between the components reveal how they connect together, and to a source of power, so they perform a specific function or operation. This book deals mostly with schematics. Figure 1-2 is a simple example.
图 1-2 示意图，包括一个电池、一个电阻器和一个电流表（标记为 A）。
FIG. 1-2 Schematic that includes a battery, a resistor, and an ammeter (labeled A).
•图示（有时也称为布局图）显示了电路板或机箱上元件的物理排列，以便于识别、安装、测试或更换。有些此类“图示”是实际照片。但请记住，图片很少能展现电路或系统中发生的电气事件。图 1-3是一个简单的示例。
• A pictorial diagram (sometimes called a layout diagram) shows the physical arrangement of the components on a circuit board or chassis so you can identify them for installation, testing, or replacement. Some such “diagrams” are actual photographs. Keep in mind, however, that pictures rarely reveal the electrical events that occur in a circuit or system. Figure 1-3 is a simple example.
图 1-3 磁性实验测试电路的物理布局示意图。
FIG. 1-3 Pictorial drawing that shows the physical layout of a test circuit for magnetism experiments.
框图
Block Diagrams
框图可以帮助你理解系统的工作原理，并在系统出现故障时帮助你进行故障排除。每个方框都有一个标签，用于描述或命名它所代表的电路，但它并不解释电路的工作原理，也不描绘各个组件。当你对电路有了基本的了解后，就可以使用框图来帮助你进行故障排除。通过查看系统的框图可以了解其运行方式，您可以查阅各个电路原理图以获取更多详细信息。请看以下两个例子。
A block diagram can help you understand how a system works, and can help you troubleshoot it when it malfunctions. Each block has a label that describes or names the circuit it represents, but it doesn’t explain the workings of the circuit, nor does it depict the individual components. When you gain a general understanding of how a system operates by examining its block diagram, you can consult each of its circuit schematics for more details. Consider two examples.
• 你想设计一个电子设备来执行特定任务。你可以先绘制一个框图来简化设计过程，框图会展示完成项目所需的所有电路。然后，你可以将每个框图扩展成原理图。最终，你会得到一个完整的原理图，它不仅取代了所有框图，还详细地展示了整个设备。
• You want to design an electronic device to perform a specific task. You can simplify the process by drawing a block diagram that shows all the circuits you’ll need to complete the project. Then you can expand each block into a schematic. In the end, you’ll have a complete schematic that replaces all the blocks and shows the whole device in detail.
或者，你可以反过来思考这个问题。假设你有一个复杂的原理图，你想用它来……排查设备故障。由于原理图显示了所有组件，您可能难以确定设备的哪个部分出现问题。框图可以帮助您了解每个电路如何与其他电路协同工作。借助框图找到故障电路后，您可以查看其原理图并进行测试，以隔离故障组件。
• Alternatively, you can approach the task the other way around. Imagine that you have a complicated schematic, and you want to use it to troubleshoot a device. Because the schematic shows every single component, you might find it difficult to determine which part of the device has the problem. A block diagram can help you envision how each circuit works in conjunction with the others. Once you’ve found the troublesome circuit with the aid of the block diagram, you can examine its schematic and do tests to isolate the faulty component.
原理图
Schematic Diagrams
原理图就像电路的“地图”，展示了所有元件及其相互连接方式。根据一本常用词典的解释，“原理图”一词意为“与方案有关的；图解的”。因此，任何描绘方案（电子、生理、地理或其他任何方案）的图纸都可以称为原理图。
A schematic acts as a “map” of a circuit, showing all of the individual components and how they interconnect with one another. According to one popular dictionary, the term schematic means “of or relating to a scheme; diagrammatic.” Therefore, you can call any drawing that depicts a scheme (electronic, physiological, geographic, or whatever) a schematic diagram.
最常见的原理图类型之一是用于汽车的道路地图。该地图可能显示城镇内、州或省内，甚至跨多个州或省的所有可通行路线。与电子电路原理图类似，道路地图显示了与特定地理区域相关的所有地标。在电子领域，原理图使技术人员能够在测试、故障排除和维修小型电路、大型设备或庞大系统时，推断出各个组件及其连接方式。
One of the most common types of schematic is a road map for use in motor vehicles. The map might show all the navigable paths of travel inside a town, within a state or province, or across multiple states or provinces. Like a schematic of an electronic circuit, a road map shows all the landmarks relevant to a geographic region. In electronics, a schematic allows a technician to extrapolate the components and interconnections when testing, troubleshooting, and repairing a small circuit, a large device, or a huge system.
假设你想开车从一处地点前往另一处地点。你的路线图显示了这两个地点之间的所有地标。相比之下，电路图显示了电子电路中任意两点之间的所有元件。但这两个图都不仅仅表示点。你需要知道的不仅仅是两个固定地点之间有哪些城镇，才能了解该地区的整体情况。你可以记下沿途各个城镇或地标的名称，但这样的清单无法取代一张好的路线图。从电子学的角度来看，你也可以通过编制特定电路中的元件清单来达到同样的目的，例如：
Suppose that you want to drive your truck from one place to another. Your road map shows all the landmarks between these two locations. By comparison, a schematic shows all the components between any two points in an electronic circuit. But both diagrams indicate more than mere points. You need to know more than which towns lie between two fixed locations to get an idea of the overall nature of the region. You could write down the names of the various towns or landmarks along a chosen route, but such a list couldn’t take the place of a good road map. From an electronics standpoint, you could do the same thing by compiling a list of the components in certain circuit, such as:
• 两个 120 欧姆电阻
• Two 120-ohm resistors
• 一个 1000 欧姆电阻器
• One 1000-ohm resistor
• 一个 PNP 晶体管
• One PNP transistor
• 两个 0.47 微法拉电容器
• Two 0.47-microfarad capacitors
• 90厘米长的连接线
• 90 centimeters of hookup wire
• 一块 6 伏“手电筒”电池
• One 6-volt “lantern” battery
• 一个带内置断路器的开关
• One switch with a built-in circuit breaker
这份清单列出了电路的“组成元件”，但没有提供任何功能方面的信息。你知道构建电路所需的所有元件，但你不知道组装起来之后电路会做什么！事实上，你可以用几种不同的方式组合这些元件，从而构建出功能各异的电路。
This list tells you the “ingredients” of the circuit, but nothing in a functional sense. You know all the components necessary to build the circuit, but you don’t know what it will do when you put it together! In fact, you might combine these components in several different ways to make circuits that do different things.
电路图不仅要显示电路中的所有元件，还要显示这些元件之间的工作原理。就像地图用代表街道和公路的线条连接城镇和其他兴趣点一样，表示二级公路的线条与表示四车道高速公路的线条也不同。通过练习，你可以一眼看出哪些线条代表哪些类型的道路。在电子学中，电路图使用实线表示普通的导电体，例如导线或箔片；其他类型的线条（或线条组）则表示电缆、逻辑路径、屏蔽罩和无线链路。绘制互连线或线条组时，你实际上是在描述连接元件之间的某种关系。
A schematic must not only show all the components in a circuit, but also how these components work with each other. A road map connects towns and other points of interest with lines that represent streets and highways. A line that indicates a secondary road differs from a line that represents a four-lane highway. With practice, you can learn to tell at a glance which sorts of lines indicate which types of roads. In electronics, a schematic uses a solid line to indicate a plain electrical conductor such as a wire or foil run; other types of lines (or sets of lines) represent cables, logical pathways, shielding enclosures, and wireless links. Whenever you draw an interconnecting line or set of lines, you portray some relationship between the connected components.
原理图符号
Schematic Symbology
示意图利用符号来展现系统的结构。在道路地图上，许多符号都是用来表示道路的线条。当然，一条代表522号州际公路的黑线，与你实际驾驶时看到的公路景象截然不同！你只需要知道这条线代表522号州际公路即可，其他细节可以自行想象。如果一定要在纸质道路地图上查看公路的示意图，那么这些地图占用的空间将是你在车里存放的折叠纸地图的数千倍。
A schematic uses symbology to reveal the anatomy of a system. On a road map, many of the symbols are lines to indicate roadways. But of course, a single black line that portrays State Route 522 doesn’t resemble the appearance of this highway as you drive along it! You need only know the fact that the line symbolizes State Route 522. You can make up the other details in your mind. If you always had to see pictorial drawings of highways on paper road maps, those maps would take up thousands of times more space than the folded-up papers that you keep in your vehicle.
在一张制作精良的公路地图上，你会看到一个符号图例。图例会显示每个符号，并用简单的语言解释它们的含义。例如，如果地图上画着一架小飞机代表一个机场，而你记住了这一点，那么每次看到飞机符号，你就知道地图上所示的位置有一个机场。符号系统就是用另一个实物（例如飞机图像）来表示一个实物（例如机场）。
On a well-produced road map, you’ll find a key to the symbols. The key shows each symbol and explains in simple language what each one means. If a small airplane drawn on the map indicates an airport and you memorize this fact, then each time you see the airplane symbol, you’ll know that an airport exists at that particular site as shown on the map. Symbology depicts a physical object (such as an airport) in the form of another physical object (such as an airplane image).
一张地图包含许多不同的符号。每个符号都是经过“精心设计”的，旨在让用户能够理解其含义。例如，当你在地图上看到一架小型飞机时，你很可能知道这个地点与飞机有关，因此不需要详细的解释。但如果地图制作者用啤酒瓶来代表机场，那么任何没有阅读图例的人很可能会想到酒吧，而不是机场！由于地图需要许多不同的符号，优秀的地图制作者会努力确保这些符号的含义清晰明了。
A road map contains many different symbols. Each symbol is “human engineered” to make sense in your mind. For instance, when you see a miniature airplane on a road map, you’ll probably know that this location has something to do with airplanes, so you won’t need a detailed explanation. If, on the other hand, the mapmaker used a beer bottle to represent an airport, anyone who failed to read the key would probably think of a saloon, not an airport! Because a map needs many different symbols, a good mapmaker tries to make sure that the symbols make sense.
逻辑思维在设计表示复杂事物的方案时只能起到一定作用，尤其是在电子电路和系统领域。例如，圆（有时是椭圆）通常是晶体管符号、可控硅整流器 (SCR) 符号和电源插座符号的基础。圆内的其他符号则表明它代表的是哪种类型的元件。
Logical thinking will only take you to a certain point in devising schemes to represent complicated things, especially when you get into the realm of electronic circuits and systems. For example, a circle (or sometimes an ellipse) normally forms the basis for a transistor symbol, a silicon-controlled rectifier (SCR) symbol, and an electric outlet symbol. Additional symbols inside the circle reveal which type of component it represents.
在电子学发展的早期，工程师们使用包含各种电极符号的圆圈来表示真空管。（现在有时仍然如此！）晶体管已经发展成为大多数情况下取代真空管的工具，因此晶体管的电路符号也以圆圈开头。电极标记仍然像以前一样位于圆圈内，但晶体管元件与真空管元件不同，因此晶体管圆圈内的标记与真空管符号中的标记不同。晶体管执行许多与真空管相同的功能（有时现在仍然如此！），因此它们的符号看起来有些相似，但它们远非完全相同。
In the olden days of electronics, engineers used circles containing various electrode symbols to represent vacuum tubes. (Sometimes they still do!) Transistors have evolved to replace vacuum tubes in most situations, so the schematic symbol for a transistor also starts with a circle. Electrode markings go into the circle as before, but transistor elements differ from tube elements, so transistor circles contain different markings than tube symbols did. Transistors perform many of the same functions as vacuum tubes did (and sometimes still do!) so their symbols look somewhat alike, but they’re far from identical.
电路图符号的用法存在不一致之处，因此电子相关的图表可能比你见过的任何路线图都要复杂和微妙得多。例如，你可以用一个圆圈来表示可控硅整流器（SCR），圆圈内有一个二极管符号，并延伸出一条线。但SCR的功能与电子管或晶体管的功能不同。电源插座是另一个例子。它的工作原理与电子管、晶体管或SCR完全不同，但它的符号基础也是一个圆圈，就像电子管、晶体管或SCR的符号一样。你将在第三章中学习更多关于电路图符号的知识。
Inconsistencies arise in schematic symbology, so electronics-related diagrams can get a lot more sophisticated and subtle than any road map you’ll ever see. For example, you can portray an SCR as a circle with a diode symbol inside and an extra line coming out of it. But an SCR performs a function that differs from what a tube or transistor does. An electric outlet can serve as another example. It doesn’t work anything like a tube or transistor or SCR, but the basis for the symbol is a circle, just like the circle for a tube or transistor or SCR. You’ll learn more about schematic symbols in Chapter 3.
图 1-4 A 为包含圆圈的 PNP 双极型晶体管的示意图符号。B 为不带圆圈的相同符号。
FIG. 1-4 At A, the schematic symbol for a PNP bipolar transistor including a circle. At B, the same symbol without the circle.
元件互连
Component Interconnections
考虑一种常见的电子元件：PNP 双极型晶体管。这种器件有三个电极元件，虽然存在许多不同类型的 PNP 双极型晶体管，但它们的符号绘制方式几乎相同。你可能会在成千上万种不同的电路中找到 PNP 双极型晶体管！一个好的电路图应该描述：
Consider a single, commonplace electronic component: a PNP bipolar transistor. This device has three electrode elements, and although many different varieties of PNP bipolar transistors exist, you draw all their symbols in pretty much the same way. You might find a PNP bipolar transistor in any one of thousands of different circuits! A good schematic will describe:
• 该特定元件如何融入电路中。
• How that particular component fits into the circuit.
• 还有哪些其他组件与它协同工作？
• Which other components work in conjunction with it.
• 哪些其他电路元件的正常工作依赖于它？
• Which other circuit elements depend on it for proper operation.
PNP型双极晶体管可以用作开关、放大器、振荡器或阻抗匹配器件。如果某个PNP型双极晶体管在某个电路中用作射频（RF）放大器，这并不意味着它只能用作射频放大器，而不能用于其他用途。例如，你可以将它从射频放大器电路中取出，放入另一个电路中，用作音频（AF）振荡器的核心元件。
A PNP bipolar transistor can act as a switch, an amplifier, an oscillator, or an impedance-matching device. If a PNP bipolar transistor functions in some circuit as a radio-frequency (RF) amplifier, you can’t conclude that a PNP bipolar transistor can operate as an RF amplifier only, and nothing else. For example, you could pull the thing out of the RF amplifier circuit and put it into another circuit to serve as the “heart” of an audio-frequency (AF) oscillator.
想象一下，你决定开车从马里兰州巴尔的摩前往加利福尼亚州洛杉矶。即使你过去曾多次走过这条路线，你也可能记不清所有需要走的路线以及沿途经过的城镇。（如果你已经很久没走过这条路线，它们可能已经发生了变化！）一张最新的路线图可以让你对整个行程有一个大致的了解。由于所有行程数据都以你可以一目了然的形式呈现，路线图在帮助你了解整个行程方面发挥着至关重要的作用，而不是让你逐一了解每个环节。电路图对于理解电子电路的“行程”也起到同样的作用。而且，就像路线图一样，随着工程师对原始设计的改进，电路图也会随着时间的推移而不断演变。
Imagine that you decide to drive your car from Baltimore, Maryland to Los Angeles, California. Even if you’ve made the trip several times in the past, you probably don’t recall all the routes that you’ll need to take and all the towns and cities that you’ll pass along the way. (They might have changed, anyway, if you haven’t made the trip for some time!) An up-to-date road map will give you an overall picture of the whole trip. Because all the trip data exists in a form that you can scan at a glance, the road map plays a critical role in allowing you to envision the entire trip rather than each and every piece, one at a time. A schematic does the same thing for a “trip” through an electronic circuit. And, like road maps, schematics can evolve over time as engineers make improvements to the original design.
继续以路线图和横跨美国之旅为例，假设你已经记住了从巴尔的摩到洛杉矶的整条路线。再假设沿途的一条主要高速公路正在施工，迫使你选择其他路线。如果没有路线图，你将完全不知道该地区还有哪些道路，该选择哪条替代路线，以及哪条绕行路线能让你尽可能地保持原路。最终将您送回原旅行路线，最大程度地减少延误和不便。
Continuing with the road map and the coast-to-coast trip as an example, imagine that you’ve memorized the entire route from Baltimore to Los Angeles. Assume also that one of the prime highways along the way has gone under construction, forcing you to take an alternate route. Without a road map, you’ll have no idea what other roads exist in that area, which alternate route to take, and which detour will keep you on course as much as possible and eventually return you to the original travel route with a minimum of delay and inconvenience.
电子电路包含许多“主干道”和“支路”。有时，其中一些路径会发生故障，需要找出问题并进行修复。即使你能在脑海中想象出整个电路，你也不可能记住所有不同的电路路径，而其中一条或多条路径都可能存在缺陷。我所说的想象电路，并非指电路的原理图，而是指电路的实际元件及其连接方式，也就是所谓的硬连线。
An electronic circuit has many “highways” and “byways.” Occasionally, some of these routes break down, making it necessary to seek out the problem and correct it. Even if you can visualize the circuit in your head, you’ll find it impossible to keep in your “mind’s eye” all the different electrical paths that exist, one or more of which could prove defective. When I write of visualizing the circuit, I don’t mean the schematic equivalent of the circuit, but the circuit’s actual components and interconnections, known as the hard wiring.
电路图提供了电路的整体布局，展示了各种线路和元件之间的相互作用。当你能够了解整个电路如何依赖于每条线路和元件时，你就可以诊断和修复可能出现的任何问题。如果没有这样的视图，如果你想让故障电路重新工作，就只能“盲目摸索”。你甚至可能引入新的问题，而不是解决原来的问题！
A schematic gives you an overall map of a circuit and shows you how the various routes and components interact. When you can see how the complete circuit depends on each individual route and component, you can diagnose and repair any problem that might arise. Without such a view, you’ll have to “shoot in the dark” if you want to get a malfunctioning circuit working again. You might even introduce a new problem instead of resolving the original one!
图 1-5 一个相当复杂的电路图。读完本书后，你会觉得它很简单！（现在不用担心元件的标识。）
FIG. 1-5 A rather complicated schematic. When you’ve finished this book, you’ll think it’s simple! (Don’t worry about the component designators right now.)
视觉语言
A Visual Language
英语或其他任何语言中的每一个词都是一个复杂的符号，由被称为字符的更简单的元素构成。以“停止”这个词为例。如果没有参照物，这个声音本身没有任何意义。新生儿听到的只是你嘴里发出的声音，仅此而已！但通过学习符号系统，这个词就获得了意义，因为开始说话和理解的孩子可以将“停止”与其他词语以及动作进行比较。你甚至可以说，“停止”这个词本身就是一种符号系统中的符号。当你使用“停止”这个词时，你的意图也可以用“不要继续前进”这句话来表达。这句话本身也是一种符号系统，表达了你想要采取的行动的心理图像。
Every word in English or any other verbal language is a complex symbol made from simpler elements called characters. Let’s take the word “stop,” for example. Without a reference key, this sound means nothing. A newborn infant hears noise coming out of your mouth, that’s all! But through learning the symbology, this word acquires meaning because the child, who has begun to speak and understand, can compare “stop” to other words, and also to actions. You can even say that the word “stop” is a sort of symbology within symbology. Your intent, when using the word “stop,” can also be expressed by the phrase “Do not proceed further.” This phrase also constitutes symbology, expressing a mental image of a desired action.
如果人们能够通过心灵感应进行交流，那么语言及其符号就变得不再必要。思考的速度远超说话、阅读或写作的速度。无论一个人在说话、阅读或写作时使用何种语言，其大脑运作过程都是相同的。新生儿不会说话，也不会理解任何语言。但无论这个婴儿出生在美国、南非、中国、印度还是其他任何地方，他的思维过程都是相同的。
If people could communicate by mental telepathy, then no one would need language or the symbols that it comprises. Thinking happens faster than anyone can speak or read or write. Brain processes are the same from human to human, regardless of what language any particular person employs when speaking, reading, or writing. A newborn baby speaks and understands no language. But whether that baby was born in America, South Africa, China, India, or wherever, the same thought processes take place.
婴儿天生就知道何时饥饿、疼痛、恐惧或快乐。他们无需语言就能理解这些状态。但婴儿从一开始就必须进行交流。因此，所有新生儿都使用同一种语言进行交流（主要是哭和笑）。随着婴儿通过更完善的感官（眼睛、耳朵、鼻子、手指）更好地理解周围环境，他们收集的信息也越来越多。这时，各种语言开始发挥作用，不同的社会使用不同的语言符号来表达心理过程。然而，人脑仍然像以前一样进行着非语言的思维过程，因为仅仅依靠符号进行思考会消耗太多时间和“脑容量”。
A baby knows when it’s hungry, in pain, frightened, or happy. It needs no language to comprehend these states. But the baby does have to communicate right from the start. For this reason, all newborns communicate in the same language (crying and laughing, mostly). As babies comprehend more of their environment through improved sensory equipment (eyes, ears, nose, fingers), they collect more data. Then the various languages come into play, with different societies using different verbal symbols to express mental processes. The human brain nevertheless carries on the same nonlinguistic thought processes as before, because thinking in terms of symbols alone would take too much time and “brain storage.”
大脑帮助人类将复杂的思想转化为语言，反之亦然，就像计算机将编程语言翻译成电子脉冲，反之亦然一样。想象一下，一个孩子即将走到一辆疾驰的汽车前。如果你的大脑需要以符号形式处理数百万个数据元素，你将花费大量时间等待大脑传递正确的处理信息，而那个孩子很可能在你采取任何行动之前就已经被撞死了。相反，你的大脑会快速扫描所有感官器官接收到的数据，然后将其汇总成一个用于交流的单一符号。在上述情况下，一个清晰可闻（最好是响亮）的符号就是“停！”。当你看到一个孩子即将走到车流中时，你可能会喊出这个词，并在孩子的大脑中引发相应的处理过程。
The brain helps a human to transpose complex thoughts into language and vice-versa, just as a computer translates programming languages into electronic impulses and vice-versa. Imagine that a child is about to step in front of a speeding automobile. If your brain had to handle millions of data elements symbolically, you would spend a lot of time waiting for your brain to deliver the correct processed information, and that child would probably get killed before you could take any action. Rather, your brain scans all the data received by your sensory organs in quick time and then sums it up into a single symbol for communication. A good audible (and hopefully loud) symbol in the above-mentioned case is “Stop!” You, seeing a child about to walk into heavy traffic, might shout that word and produce in the child’s brain the appropriate sequences of processes.
并非所有语言都包含口语词汇。你肯定听说过手语，也就是通过手臂和手的动作来表达意思。如果你玩过业余无线电，尤其是如果你和我一样在上世纪60年代拿到了业余无线电执照，你肯定知道摩尔斯电码，它是一套通信符号。在大多数情况下，仅由视觉符号或听觉符号组成的语言，对我们人类来说，效率远不如由视觉和听觉符号结合而成的语言。以“停止”这个符号为例，你可以用多种不同的方式表达这个词。这个词本身就有意义，但我们表达的方式（我们的“语气”）会增强它的含义。无论是纯文本还是摩尔斯电码，你都无法用印刷体或可听见的S、T、O和P这些字符来表达所有这些含义。
Not all languages involve spoken words. You’ve doubtless heard of sign language, whereby a person’s arms and hands move to communicate ideas. If you’ve done any amateur (“ham”) radio communication, especially if you got your “ham” license back in the time when I got mine (the 1960s), you know the Morse code as a set of communication symbols. In most instances, a language comprising only visual symbols or audio symbols is not as efficient for us humans as one composed of visual and audio symbols combined. Using the symbol “stop” again, you can utter this word in many different ways. The word in itself means something, but the way we say it (our “tone of voice”) augments the meaning. You can’t do all that with the printed or audible characters S, T, O, and P in plain text or in Morse code.
我们人类已经发展出一些通用的方法来修改视觉符号。例如，我们经常将颜色与口语词汇的视觉符号结合起来使用。想想“停止”标志。它是红色的，对吧？人们往往会将红色与“停止”或“危险”联系起来。再想想“让行”标志。它是黄色的，代表着需要注意，但力度不如红色那么强烈；意思是“谨慎通行”。当交通信号灯变成绿灯时，你可以“走！”（但考虑到现在有些傻瓜开车的方式，如果你想长寿，最好时刻小心谨慎。）
We humans have arrived at universal methods of modifying visual symbols. For example, we often use color in conjunction with the visual symbol for a spoken word. Think of a “stop” sign. It’s red, right? People tend to associate red with the word “stop” or “danger.” Or think of a “yield” sign. It’s yellow, representing something that demands attention, but in a less forceful way than red does; you “proceed with caution.” When a traffic light turns green, you can “go!” (But considering how some fools drive nowadays, you’d better use caution all the time if you want to live very long.)
电路图也不适用于任何形式的口头（可听见的）符号系统。例如，当你在电路图中看到场效应晶体管（FET）的符号时，你不会听到纸或电脑说：“天哪，是场效应晶体管，不是双极型晶体管！”你必须确保正确解读符号。如果你想搭建电路，却错误地把双极型晶体管放在了应该放置 FET 的位置，那么最终的设备或系统就无法正常工作。某些元件可能会烧毁，所以当你意识到错误，把双极型晶体管和 FET 放在一起时，你必须先对整个电路进行故障排除才能继续使用。你甚至可能需要从头开始，更换每一个元件！
Schematics don’t lend themselves to any form of oral (audible) symbology either. When you see the symbol for, say, a field-effect transistor (FET) in a schematic diagram, you don’t hear the paper or computer say, “Field-effect transistor, for heaven’s sake, not bipolar transistor!” You have to make sure that you read the symbol correctly. If you want to build the circuit and you mistakenly put a bipolar transistor where an FET should go, then you can’t expect the final device or system to work. Something might burn out, so that when you recognize your error and bipolar transistor with an FET, you’ll have to troubleshoot the whole circuit before you can use it. You might even have to start all over again and replace every single component!
你的感官和你的中央处理器（你的大脑）使你难以通过直接操作电子电路来全面理解其工作原理。你必须循序渐进地接收数据，将其整理成纸质形式（通过符号系统），并提供纸质输出。你可以将这种方法比作儿童练习册中的“连点成线”游戏。单个点毫无意义，但一旦它们按照逻辑排列并用线连接起来，你就能得到一幅完整的图像。点之间的关系以及它们连接的顺序包含了你需要知道的一切。
Your senses along with your central processor (your brain) render you less than proficient at mentally conceiving all the workings of electronic circuits by dealing with them directly. You must accept data one small step at a time, compiling it in hardcopy form (through symbology) and providing a hardcopy readout. You can liken this method to “connect-the-dots” drawings in children’s school workbooks. Individually, the dots mean nothing, but once they’re arranged in logical form and connected by lines, you get an overall picture. The dots’ relationships to each other and to the sequence in which they’re connected tell you all you need to know.
本书剩余章节首先介绍各个电子元件的符号，然后讲解简单的电路，最后展示一些较为复杂的电路。电路图符号和图表是为人类设计的，因此人类的逻辑在确定哪些符号代表哪些事物方面起着至关重要的作用。从这个角度来看，电路图的创建和阅读……示意图类似于数学，特别是传统的平面几何！
The remaining chapters in this book start with the symbols for individual electronic components, then move on to simple circuits, and finally show you a few rather complicated circuits. Schematic symbols and diagrams are designed for humans, so human logic plays a prime role in determining which symbols mean which things. In that respect, the creation and reading of schematic diagrams resembles mathematics, and in particular, old-fashioned plane geometry!
2
2
框图
Block Diagrams
框图描绘了设备或系统的总体结构。这种图通过将复杂系统的主要部分分离出来，并展示它们如何相互连接和交互，从而简化了系统的运作方式。在计算机工程中，框图可以帮助您理解程序或其他进程的工作原理。
A block diagram portrays the general structure of a device or system. Such a diagram can provide a simplified rendition of a complicated system by separating its main parts and showing you how they interconnect and interact. In computer engineering, block diagrams can help you envision how programs or other processes work.
一个简单的例子
A Simple Example
图 2-1显示了一个框图，该装置可以将交流电(AC)（例如您家中电源插座上的那种电流）转换为直流电(DC)（例如电化学电池产生的那种电流）。业余爱好者和专业人士将这种类型的装置称为电源。
Figure 2-1 shows a block diagram of a device that converts alternating current (AC), of the sort you find at the electric outlets in your house, to direct current (DC), of the sort you get from an electrochemical battery. Hobbyists and professionals call this type of device a power supply.
图 2-1 为交流-直流转换器（也称电源）的框图。您自然会发现电流是从左向右流动的，因此图中的线条没有箭头。
FIG. 2-1 Block diagram of an AC-to-DC converter, also called a power supply. You’ll naturally sense that the electricity flows from left to right, so the lines have no arrows.
最左侧的接线端子接收交流输入。从左到右，电流依次经过变压器、整流器和滤波器，最终以纯直流电的形式输出。图中各方框之间的连线没有箭头；绘制者认为无需箭头即可判断电流方向。
The terminal at the far left accepts the AC input. As you go from left to right, the electricity passes through the transformer, the rectifier, and the filter before arriving at the output as pure DC. In this case, the lines between blocks have no arrows; the diagram’s creators assume that you can sense the process direction without them.
功能图
Functional Drawings
框图可以表示大型设备中各个小型电路之间的互连，或者大型系统中不同设备之间的互连。当您看到如图2-1所示的框图时，您可以将其称为功能图，因为它能告诉您一些关于设备功能的信息（但并不全面）。如果您想了解更多细节，则需要查看原理图。
Block diagrams can indicate the interconnections among small circuits in a larger device, or among diverse devices in a massive system. When you see a block diagram rendered in the style of Fig. 2-1, you can call it a functional diagram because it tells you something (but not a lot) about what the device does. If you want to know more detail, you’ll need to see the schematic.
想要设计复杂电子系统的工程师可以从框图入手。框图展示了运行设备中的所有电路部分（阶段），但并不包含这些阶段的内部细节。接下来，工程师会绘制电路原理图，将电路填充到每个框图中，并实现相应的功能。第一个框图会被它所代表的电路原理图替换。工程师按照功能顺序依次处理各个框图，创建可用于构建系统每个阶段的原理图。当所有框图都被原理图替换后，就形成了一个详细的（但目前仍停留在理论层面的）系统设计。
An engineer who wants to design a complex electronic system can start with a block diagram. It shows all the circuit sections (stages) in a functioning device, but none of the internal details of those stages. Then the engineer develops schematics of circuits that fill each block and serve the appropriate function. The first block gets replaced by the schematic of the circuit it represents. The engineer proceeds through the blocks in functional order, creating schematics that you can use to build each stage in the system. When every block has been replaced with a schematic, a detailed (but so far only theoretical) system design exists.
使用框图的另一种方法是从系统的完整原理图入手。假设原理图非常复杂，并且由于某种未知原因，系统无法按工程师预期的方式运行。虽然原理图可以描述电子系统的功能，但就此而言，它不如功能框图清晰。原理图包含的信息实在太多了！如果没有框图，维修技术人员就必须从原理图入手，费力地识别系统中的每个阶段，然后将整个系统绘制成框图。完成后，框图将揭示每个阶段如何与其他阶段交互。使用这种方法，技术人员可以识别出一个或多个可能存在故障的阶段，并参考原始原理图对这些可疑电路进行测试。
Another way of using block diagrams involves starting with the complete schematic of a system. Imagine that the schematic is quite complicated, and for some unknown reason the system doesn’t work as the engineer thinks it should. Although a schematic can describe the functioning of an electronic system, it’s not as clear as a functional block diagram for that purpose. The schematic literally has too much information! Lacking a block diagram, a repair technician would have to start with the schematic, laboriously identify each stage in the system, and then draw the entire system diagram in block form. When finished, the block diagram would reveal how each stage interacts with the others. Using this method, the technician could identify one or more stages as likely trouble zones, and refer back to the original schematic to conduct tests in those suspect circuits.
您可以使用框图来描述特定类型无线电系统的运行原理，例如调幅（AM）语音发射机。当然，不同制造商生产的AM发射机没有两台是完全相同的，但它们都包含类似的功能级。不同类型的振荡器工作方式可能有所不同，但所有振荡器的功能都相同：产生射频信号！当您想要了解或描述功能基本相同的电路之间的细微差别时，就需要绘制所有电路的原理图。
You can describe the operation of a specific type of radio system, for example, an amplitude-modulated (AM) voice transmitter, by means of a block diagram. Of course, no two AM transmitters built by different manufacturers are identical, but all of them contain similar functional stages. One type of oscillator might work differently from another type, but all oscillators do the same thing: generate an RF signal! When you want to know or portray small differences among circuits that do essentially the same things, then you need schematics of them all.
图 2-2的框图展示了一个频闪灯系统，其结构与套件组装手册中的示意图类似。该套件包含独立电路、一套电缆和一份说明书。您需要按照说明书中的步骤，将电缆（带箭头的实线）连接到套件提供的各个独立电路（模块）之间。
The block diagram of Fig. 2-2 shows a strobe light system as you might see it in the assembly manual for a kit comprising self-contained circuits, a set of cables, and an instruction manual. You connect the cables (solid lines with arrows) among the self-contained circuits (blocks) provided with the kit, meticulously following the instructions in the manual.
图 2-2 为频闪灯供电电路的框图。箭头表示电流的流动方向。
FIG. 2-2 Block diagram of a circuit designed to provide power to a strobe light. Arrows show how the electricity flows.
输入信号从左侧进入；它是市电交流电，例如标准墙壁插座提供的交流电。在美国，这种交流电的标称电压为 117 伏 (117 V)，频率为 60 赫兹 (60 Hz)，其中“赫兹”表示“每秒周期数”。（在一些国家，电压约为 234 伏，而在另一些国家，频率则为 50 赫兹而非 60 赫兹。）输入的交流电会先经过一个保险丝，然后再连接到一组用于提供定时功能的元件。
The input signal enters at the left; it’s utility AC such as you get from a standard wall outlet. In the United States, this AC has a nominal voltage of 117 volts (117 V) and a frequency of 60 hertz (60 Hz), where “hertz” means “cycles per second.” (In some countries the voltage is about 234 V, and in some countries you’ll find a frequency of 50 Hz rather than 60 Hz.) The input AC goes to a fuse, and also to a combination of components that provide timing.
顶部路径（即您看到的保险丝所在位置）通向一个整流器，其输出连接到一个三端频闪灯的一个端子。整流器的输出还连接到一个可调定时器，该定时器提供可变的闪烁频率。灯泡。定时器的输出连接到变压器，变压器再连接到灯泡的另外两个接线端子。您无需了解“A”、“T”和“K”这些标识的含义；您只需在组装套件时知道如何连接电缆即可！有些人把这种“照着做”的指导方式称为绘制接线图。
The top path, where you see the fuse, leads to a rectifier whose output passes to one terminal of a three-terminal strobe lamp. The rectifier output also connects to an adjustable timer that provides a variable flash rate for the lamp. The timer output goes to a transformer, which in turn connects to two more lamp terminals. You don’t have to know what the designators “A,” “T,” and “K” mean; you need only know how to hook up the cables as you assemble the kit! Some people call this sort of “monkey see, monkey do” instructional drawing a wiring diagram.
电流和信号路径
Current and Signal Paths
图 2-3是一个电源的框图，该电源可产生多个具有不同电气特性的输出。按照图中箭头所示，从左侧（输入端）向右下方（输出端）依次查看，您会发现该系统使用 117 伏交流电 (117 VAC) 工作，这在美国的公共插座中很常见。整个电源可以安装在一个机柜中，只需一根电源线和一个插头即可连接到墙壁插座，并配有用于连接多个设备的螺丝端子。
Figure 2-3 is a block diagram of a power supply that produces several outputs having various electrical characteristics. As you proceed through the diagram from the left-hand end (the input) to the right and downward (the outputs) according to the arrows, you’ll see that the system operates from 117 volts AC (117 VAC), commonly found at utility outlets in the United States. The entire power supply could reside in a single cabinet with a single cord and plug for a wall outlet and screw-on terminals for connection to multiple devices.
图 2-3 产生几种不同输出的电源的框图。
FIG. 2-3 Block diagram of a power supply that produces several different outputs.
输入的交流电被分成两条相同的路径，两条路径的电压均为 117 VAC。一条分路器的输出连接到“下”变压器，该变压器提供 16 VAC 和 3 VAC 的输出。另一条分路器的输出连接到“上”变压器，该变压器的输出连接到：
The input AC gets split into two identical paths, both at 117 VAC. One splitter output goes to the “lower” transformer that provides 16 VAC and 3 VAC output. The other splitter output runs to the “upper” transformer, which goes to:
• 一款“顶部”整流器/滤波器，提供 +12 伏直流电 (+12 VDC)，无需稳压功能。
• A “top” rectifier/filter that provides +12 volts DC (+12 VDC) without voltage regulation
• 断电检测器，例如交流电压表或报警器
• A power “off” detector, such as an AC voltmeter or alarm
• 一种“底部”整流器/滤波器，可提供 +18 VDC 电压，无需稳压。
• A “bottom” rectifier/filter that provides +18 VDC without voltage regulation
此外，“底部”整流器/滤波器输出连接到稳压器，无论家用电压从电力公司发出时出现轻微的浪涌和骤降，都能将其保持稳定的 +12 VDC。
In addition, the “bottom” rectifier/filter output connects to a voltage regulator that maintains it at a steady +12 VDC regardless of minor power surges and dips in your household voltage as it comes from the utility company.
图 2-4是一个简单的 AM 无线电发射机的框图。你对着麦克风说话，声音信号会经过一个音频前置放大器，从而被接收。信号功率适中（但不会过大）。第二个音频放大器能让你的声音更有“冲击力”！音频匹配网络确保语音信号能以尽可能大的功率传输到调制器/放大器，该调制器/放大器的射频能量来自一个振荡器，其频率由石英晶体决定。射频调制器/放大器的瞬时输出功率会根据瞬时音频输入电平而波动，从而产生调幅信号，该信号通过射频调谐网络传输到天线。
Figure 2-4 is a block diagram of a simple AM radio transmitter. You speak into the microphone, which leads to an AF preamplifier to give your voice signal some power (but not much). A second AF amplifier gives your voice a lot of “punch”! The AF matching network ensures that the voice signal will deliver the most possible power to the modulator/amplifier, which receives its RF energy from an oscillator whose frequency is determined by a quartz crystal. The instantaneous RF modulator/amplifier output power fluctuates in accordance with the instantaneous AF input level to produce an AM signal, which passes through an RF tuning network to the antenna.
图 2-4 AM 无线电发射机的框图。
FIG. 2-4 Block diagram of an AM radio transmitter.
流程图
Flowcharts
框图可以描述电子系统的工作原理，但在计算机领域，另一种称为流程图的图表可以描绘程序或软件的运行过程。流程图类似于框图，区别在于其符号体系适用于计算机的各个部分。程序是一种无形的东西（与电子系统这种有形的东西相对）。流程图以图形方式表示计算机执行程序时所采取的逻辑步骤。软件工程师根据规范绘制流程图，并根据用户需求的变化修改流程图。
Block diagrams can describe how electronic systems work, but in the world of computers, another form of diagram, called a flowchart, can portray the functioning of a program or software. A flowchart resembles a block diagram, except that the symbology applies to the sections of a computer program, an intangible thing (as opposed to an electronic system, a tangible thing). A flowchart provides a graphic representation of the logical steps that a computer takes as it executes a program. Software engineers prepare flowcharts in conjunction with specifications, and modify the flowcharts as user requirements change.
对于复杂问题，正式的书面规范可以确保所有相关人员理解并认同问题的性质以及程序的预期结果。例如，假设一位教师（就是你！）使用计算机程序来计算学生在课程期间测验的平均分，从而确定学生的期末成绩。你将每次测验的分数输入到程序中。程序输出所有分数的平均值。图 2-5显示了程序流程图，如下所示。
For complex problems, a formal written specification can ensure that everyone involved understands and agrees on the nature of the problem, and on the desired results of the program. For example, suppose that a schoolteacher (that’s you!) uses a computer program to help determine a student’s final course grade by calculating an average from scores the student got for quizzes during the course period. You input each and every quiz score to the program. The program outputs the average of all those scores. Figure 2-5 shows a flowchart of the program process, as follows.
图 2-5 描述计算机程序的流程图。
FIG. 2-5 A flowchart that describes a computer program.
• 接收您的测验分数。
• Receive the quiz scores from you.
• 将所有测验分数加起来，得到它们的总分。
• Add up all the quiz scores to get their sum.
• 核实所有测验分数是否都已统计在内。
• Verify that you have accounted for all the quiz scores.
• 将总分除以测验次数，即可得到平均测验分数。
• Divide the sum by the number of quizzes to get the average quiz score.
• 打印平均测验分数。
• Print the average quiz score.
计算机把整个过程中最难的任务留给了你，老师：决定学生应得的成绩！如果测验很难，你可能会接受较低的平均分，并给予标准的“字母等级”（例如 A、B、C、D 或 F）；如果测验很容易，你可能会要求更高的平均分，并给予相应的等级。
The computer leaves the hardest task in the process to you, the teacher: Decide what grade the student deserves! If the quizzes were difficult, you might accept fairly low average scores for standard “letter grades” (such as A, B, C, D, or F); if the quizzes were easy, you might demand higher average scores for given grades.
流程图以图形方式呈现程序的结构，揭示步骤和路径之间的关系。当程序有许多由众多决策产生的不同路径时，流程图可以帮助您理清思路。您可以将流程图作为理解问题和辅助程序设计的工具。
The flowchart graphically presents the structure of the program, revealing the relationship among the steps and paths. When a program has many different paths that result from numerous decisions, a flowchart can help you sort things out. You can use the flowchart as a tool to understand the problem and to aid in program design.
构思和绘制一个好的流程图可能需要相当长的时间。一旦程序编写完成并绘制了流程图，再去修改流程图以反映程序的变化就可能非常困难。由于这些限制，一些程序员对流程图敬而远之，但对另一些程序员来说，流程图却能为他们理解程序提供宝贵的帮助。为了促进流程图的统一性，人们采用了标准符号。图 2-6展示了最常用的符号。在一个复杂的流程图中，你可能会用到所有这些符号。
You might need quite a lot of time to conceive and draw up a good formal flowchart. Modifying a flowchart to incorporate changes, once a program has been written and its flowchart composed, can prove difficult. Because of these limitations, some programmers shy away from flowcharts, but for others they provide valuable assistance in understanding a program. In order to promote uniformity in flowcharts, standard symbols have been adopted. Figure 2-6 shows the most common ones. In a sophisticated flowchart, you might find them all.
图 2-6 用于表示计算机程序的流程图的常用符号。
FIG. 2-6 Common symbols for flowcharts intended to represent computer programs.
椭圆形表示起始点或终止点。算术运算放在矩形框内。输入输出指令放在梯形框内。如果你想在一个更大的流程图中展示某人先前编写的程序，你不一定需要绘制整个“子程序”的流程图。或者，您可以将整个程序表示为一个扁平的六边形。如果一个方框表示一个决策，则使用菱形。五边形表示程序中会自我改变的部分。小圆圈表示处理连接点。程序中的这种连接点可以指向多个位置。如果整个流程图有多页，则使用一个形状类似棒球场本垒板的小五边形来表示流程图各页之间的连接位置。
Ovals show start or stop points. Arithmetic operations go in rectangular boxes. Input and output instructions go in trapezoids. If you want to show a program that someone wrote earlier within the context of a larger flowchart, you don’t necessarily have to draw the flowchart for the entire “subprogram.” Instead, you might represent the entire program as a flattened hexagon. If a box indicates a decision, you use a diamond shape. A five-sided box portrays a part of the program that changes itself. A small circle identifies a processing junction point. Such a point in the program can go to several places. A small five-sided box, which has the shape of the home plate on a baseball field, shows where one page of a flowchart connects to the next, if the entire flowchart has more than one page.
您应该用数字和字母标记所有中间连接点和页面外的连接点，以告诉读者所有内部字符相同的符号都相互连接。箭头指示信息流的方向。
You should label all intermediate junction and off-page connection points with numbers and letters to tell your readers that all like symbols with the same character inside connect together. Arrows indicate the direction of the flow.
图 2-7显示了一个程序的流程图，该程序复制穿孔卡片，同时打印每张卡片上的数据。让我们来追踪一下流程。程序从顶部的“开始”椭圆开始，并沿箭头方向运行。根据“开始”下方梯形中的文字，程序读取一张卡片。沿着流程图向下，程序将卡片上的内容（数据）打孔到一张空白的厚纸上，并将数据发送到打印机。然后，程序沿着虚线返回顶部，读取下一张卡片。标有“A”的圆圈表示流入点和流出点。在本例中，它们是多余的，但在复杂的流程图中，当包含所有相关的虚线时，它们会非常有用，因为那样会使流程图变得混乱。只要有卡片需要读取和打孔，程序就会重复执行。
Figure 2-7 shows a flowchart for a program that duplicates punched cards, and at the same time prints the data on each card. Let’s trace the flow. The program begins at the “Start” oval at the top and proceeds in the direction of the arrows. According to the text in the trapezoid below “Start,” the program reads a card. Proceeding on down the chart, the program punches the card’s contents (data) as holes in a blank piece of heavy paper and sends the data to a printer. The program then goes back along the dashed line to the top and reads the next card. The circles marked “A” represent inflow and outflow points. In this case they’re superfluous, but in a complicated flowchart they can prove useful when you’d get a mess by including all the applicable dashed lines. The program repeats itself as long as it has cards to read and punch.
图 2-7 为流程图，概述了用于复制穿孔卡片的程序步骤。标有“A”的圆圈表示虚线所示反馈回路中的流入点和流出点。
FIG. 2-7 Flowchart that outlines the steps in a program intended to duplicate punched cards. The circles labeled “A” represent inflow and outflow points in the feedback loop shown by the dashed line.
工艺路径
Process Paths
让我们再看一下图 2-7。假设你想修改打孔程序，让计算机忽略空白（无孔）卡片，只复制至少有一个孔的卡片。由于计算机必须对每张卡片做出判断，因此需要在流程图中添加一个决策模块。图 2-8显示了结果。
Let’s look some more at Fig. 2-7. Suppose that you want to change the card-punching program so that the computer ignores blank (hole-free) cards and duplicates only those cards that have at least one hole. Because the computer must make a decision about each card, you’ll need to include a decision block in the flowchart. Figure 2-8 shows the result.
图 2-8 带有决策块（菱形）的流程图。标有“A”的圆圈均代表一个连接点，数据按照箭头所示方向流经该连接点。
FIG. 2-8 A flowchart with a decision block (diamond). The circles labeled “A” all represent a single junction point through which data moves as shown by the arrows.
微型计算机使用多种类型的图表，这些图表主要涉及软件（操作系统和程序），而非硬件（物理组件）。在计算机领域，功能框图比原理图更为常见，数量通常也更多。从理解的角度来看，框图可以用来概括地描述机器功能，但硬件维护和维修程序需要定义明确的原理图。计算机利用了电子元件领域的最新技术，考虑到它们能够完成的所有功能，其结构相对简单。然而，从纯粹的电子学角度来看……至于原理图，计算机极其复杂。即使是最基本的计算机，也需要大量的原理图才能表示出来。
Microcomputers use many different types of diagrams that deal mostly with software (operating systems and programs) rather than hardware (physical components). In the computer world, functional block diagrams abound and are usually more numerous than schematic diagrams. From an understanding standpoint, block diagrams can serve to portray machine functions in general, but hardware maintenance and repair procedures require well-defined schematic drawings. Computers take advantage of the latest state-of-the-art developments in electronic components and are relatively simple when you consider all the things they can do. However, from a pure electronics standpoint and as far as schematic diagrams are concerned, computers are immensely complicated. You’d need a lot of pages full of schematics to represent even the most rudimentary computer.
概括
Summary
框图可以帮助你展示和理解电子电路的工作原理。它们相对容易绘制，通常只需要一支记号笔、一些纸和一把直尺（或者一个矢量图形计算机程序以及一些相关的培训）。相比之下，原理图需要更多的工具，在某些情况下，可能需要花费数小时才能绘制成易于阅读和理解的形式。
Block diagrams can help you show and understand how electronic circuits work. They’re comparatively easy to draw, usually requiring only a marking instrument, some paper, and a straight edge (or a vector-graphics computer program and a little bit of training on it). Schematic diagrams, in contrast, need more tools and can, in some cases, take many hours to render in a form that people can read and interpret.
3
3
组件和器件
Components and Devices
在道路地图上，符号表示城市、公路、机场、铁路轨道和其他地标等地理特征。同样的规则也适用于电气和电子电路图。专用符号表示导体、开关、电阻器、电容器、电感器、晶体管和其他电路元件。每当工程师发明一种元件或设备时，他们都会为其创建一个新的电路图符号。
On a road map, symbols indicate geographical features such as cities, highways, airports, railroad tracks, and other landmarks. The same rule applies to schematics in electricity and electronics. Specialized symbols portray conductors, switches, resistors, capacitors, inductors, transistors, and other circuit elements. Whenever engineers invent a component or device, they create a new schematic symbol for it.
电阻器
Resistors
电阻器是最简单的电子元件之一。顾名思义，它们会阻碍或限制电流的流动。工程师用欧姆（Ω ）作为单位来表示电阻（电流阻碍程度）。大多数实际应用中的电阻器阻值范围在约 1 欧姆到数百万欧姆之间。偶尔也会遇到阻值小于 1 欧姆，或者阻值在十亿欧姆甚至万亿欧姆的电阻器。
Resistors rank among the simplest electronic components. As the term implies, they resist or impair the flow of electric current. Engineers express resistance (the extent of current impairment) in units called ohms. Most real-world resistors have values ranging from approximately 1 ohm up to millions of ohms. Once in a while, you’ll encounter resistors with values less than 1 ohm, or values in the thousand-millions (billions) or million-millions (trillions) of ohms.
无论阻值大小，几乎所有固定电阻器的电路符号都类似于图 3-1A或3-1B。图中左右两侧（A）或上下两侧（B）的两条水平线表示从元件末端伸出的导线，称为引脚。有些电阻器带有刚性金属端子，例如引脚或接线片，这些端子不一定从元件末端伸出。
Regardless of their ohmic value, nearly all fixed resistors have schematic symbols that look like Fig. 3-1A or B. The two horizontal lines at the left and right (A) or the top and bottom (B) depict wires called leads that protrude from the ends of the physical component. Some resistors have rigid metal terminals such as pins or lugs that don’t necessarily come out of the ends.
图 3-2展示了一个两端带有导线的碳膜固定电阻器的“透明”示意图。图 3-3展示了另外两种电阻器的示意图：线绕电阻器(A) 和膜电阻器(B)。您可以将图 3-2或图 3-3中所示的任何电阻器用图 3-1中的任一符号表示。
Figure 3-2 shows a “transparent” pictorial of a carbon-composition fixed resistor with wire leads on both ends. Figure 3-3 shows pictorials of two other types of resistors: wirewound (A) and film (B). You can denote any resistor of the sort shown in Fig. 3-2 or Fig. 3-3 with either of the symbols in Fig. 3-1.
图 3-1 固定值电阻器的符号。在电路图中，它可以水平放置 (A) 或垂直放置 (B)。
FIG. 3-1 Symbol for a fixed-value resistor. In a schematic, it can appear horizontal (A) or vertical (B).
图 3-2 碳膜电阻器的“透明”示意图。
FIG. 3-2 “Transparent” pictorial of a carbon-composition resistor.
图 3-3 显示了线绕电阻器 (A) 和薄膜电阻器 (B) 的结构示意图。
FIG. 3-3 Pictorials showing the anatomy of a wirewound resistor (A) and a film type resistor (B).
可变电阻器的阻值可以通过滑动滑块或拨片来调节。您可以将阻值设置为特定值，该值将保持不变，直到您手动更改为止。在任何给定时刻，电路都会将该元件“视为”一个固定电阻器。
A variable resistor has an ohmic value that you can adjust by moving a slide or tap along the resistive element. You set the resistance to a specific value, where it remains until you deliberately change it. The circuit “sees” the component as a fixed resistor at any given time.
当电路中包含可变电阻时，电路图会显示这一事实。图 3-4显示了一个常见的双端可变电阻符号。有些可变电阻有三个端子。图 3-5显示了两种三端可变电阻的电路图符号示例，根据其构造方式的不同，它们分别被称为电位器或变阻器。
When a circuit contains a variable resistor, the schematic reveals that fact. Figure 3-4 shows a common symbol for a variable resistor with two terminals. Some variable resistors have three terminals. Figure 3-5 shows two examples of schematic symbols for a three-terminal variable resistor known as a potentiometer or rheostat, depending on the method of construction.
图 3-4 双端可变电阻器的符号。
FIG. 3-4 Symbol for a two-terminal variable resistor.
图 3-5 三端可变电阻器的符号，也称为电位器或变阻器（取决于制造方法）。在 A 处，中心端子连接到一个端端子，从而得到一个实际上的两端元件。B 处的电阻器有三个独立的端子。
FIG. 3-5 Symbols for three-terminal variable resistors, also known as potentiometers or rheostats (depending on the method of manufacture). At A, the center terminal connects to one end terminal to obtain, in effect, a two-terminal component. The resistor at B has three independent terminals.
图 3-6所示为一种线绕式可变电阻器，其内部裸露着一圈未绝缘的电阻丝。电阻器本体上有一个滑动的金属环，可以调节该金属环与线圈的不同位置。金属环通过一根柔性导线连接到两个末端引线之一。根据金属环在线圈上的位置，它会短路不同数量的线圈匝数。当金属环沿线圈向右移动时，两个末端引线之间的电阻值会减小。
Figure 3-6 shows a variable resistor of the wirewound type, manufactured to expose an uninsulated coil of resistance wire. You can adjust a sliding metallic collar, which goes around the body of the resistor, to intercept different points along the coil. A flexible conductor connects the collar to one of the two end leads. The collar shorts out more or less of the coil turns, depending on where it rests along the length of the coil. As you move the collar to the right along the wire coil, the ohmic value between the two end leads decreases.
图 3-6 为线绕可变电阻器的示意图，其可移动的中间套筒连接到其中一个固定端引线。
FIG. 3-6 Pictorial of a wirewound variable resistor with the movable middle sleeve connected to one of the fixed end leads.
图 3-7A是旋转电位器的功能图。图 3-7B显示了它的电路符号。该符号有三个不同的触点。旋转控制轴时，中心触点和两端触点之间的电阻会发生变化。图 3-8是一个典型的实际电位器的示意图。
Figure 3-7A is a functional drawing of a rotary potentiometer. Figure 3-7B shows its schematic symbol. The symbol has three distinct contact points. When you rotate the control shaft, the resistance varies between the center contact and the end contacts. Figure 3-8 is a pictorial of a typical real-world potentiometer.
图 3-7 旋转电位器的功能图 (A) 及其相应的连接示意图 (B)。
FIG. 3-7 Functional drawing of a rotary potentiometer (A) and its schematic symbol with corresponding connections (B).
图 3-8 适用于安装在电子系统（例如收音机）前面板上的电位器的示意图。
FIG. 3-8 Pictorial of a potentiometer suitable for mounting on the front panel of an electronic system such as a radio receiver.
电阻器的电路图符号本身并不能说明其阻值，也不能提供关于该元件的任何其他信息，例如额定功率或物理结构。您通常会在电阻器符号旁边看到元件的规格说明，但这些详细信息也可能出现在单独的“元件列表”中，并通过印在电路图符号旁边的字母/数字编号（例如 R1、R2、R3 等）来引用。
The schematic symbol for a resistor, all by itself, says nothing about its ohmic value, or anything else about the component such as its power rating or physical construction. You’ll often see specifications for the component written alongside the resistor symbol, but these details might instead appear in a separate “components list” and referenced to an alphabetic/numeric designation printed next to the schematic symbol (such as R1, R2, R3, and so on).
电容器
Capacitors
电容器是一种电子元件，它能阻断直流电 (DC) 而允许交流电 (AC) 通过。它们还能以电场的形式储存能量。电容的基本单位是法拉（符号为 F）。1 法拉代表一个巨大的电量，因此大多数实际应用中的电容器都以法拉的极小部分来表示：微法拉或皮法拉。1 微法拉（符号为 µF）等于百万分之一法拉 (0.000001 F)。1 皮法拉（符号为 pF）等于百万分之一微法拉 (0.000001 µF) 或万亿分之一法拉 (0.000000000001 F)。
Capacitors are electronic components that can block direct current (DC) while passing alternating current (AC). They can also store energy in the form of an electric field. The basic unit of capacitance is the farad (symbolized F). One farad represents a huge electrical quantity, so most real-world capacitors are rated in tiny fractions of a farad: microfarads or picofarads. One microfarad (symbolized µF) equals a millionth of a farad (0.000001 F). One picofarad (symbolized pF) equals a millionth of a microfarad (0.000001 µF) or a trillionth of a farad (0.000000000001 F).
图 3-9显示了固定电容器最常用的符号。弯曲的一侧应接地，或连接到电路中更接近接地的位置。有时，您会看到其他符号，例如图 3-10A或3-10B中的符号。
Figure 3-9 shows the most common symbol for a fixed capacitor. The curved side should go to electrical ground, or to the circuit point more nearly connected to electrical ground. On occasion, you’ll see alternative symbols such as those in Fig. 3-10A or B.
图 3-9 固定电容器的标准符号。曲线表示距离地更近的极板（或极板组）。
FIG. 3-9 Standard symbol for a fixed capacitor. The curved line represents the plate (or set of plates) that’s electrically closer to ground.
图 3-10 固定电容器的替代符号。A 处为空气介质；B 处为固体介质。
FIG. 3-10 Alternate symbols for fixed capacitors. At A, air dielectric; at B, solid dielectric.
电容器种类繁多。有些是无极性的，这意味着无论正负极连接都能正常工作。另一些则是有极性的，有正负极之分。连接这类电容器时，必须确保其两端的直流电压极性正确。
Many types of capacitors exist. Some are nonpolarized devices, meaning that you can connect them in either direction and they’ll work equally well. Others are polarized, having a positive and a negative lead or terminal. You must connect such a capacitor so that any DC voltage across it has the correct polarity.
除非符号包含极性标志，否则它表示的是无极性电容器，这种电容器可以由金属板包裹陶瓷、云母、玻璃、纸或其他固体非导电材料（有时也可能是空气或真空）构成。这种非导电材料称为电介质，它将元件的金属部分隔开。典型的定容电容器由两片（或几片）导电材料组成，这两片导电材料在物理上彼此靠近，但电介质层使它们在电学上相互隔离。
Unless the symbol includes a polarity sign, it indicates a nonpolarized capacitor, which can have metal plates surrounding ceramic, mica, glass, paper, or other solid nonconductive material (and sometimes air or a vacuum). The nonconductive material, known as a dielectric, separates the metal parts of the component. A typical fixed-value capacitor comprises two tiny sheets (or sets of sheets) of conductive material that lie physically close to each other but are kept electrically apart by the dielectric layer.
图 3-11显示了极性电容器的符号。它看起来与无极性电容器的符号相似，只是在一侧多了一个加号 (+)。加号表示元件的正极应连接到外部电路中电压较高的部分。有时，符号的另一侧会出现减号 (−)，而不是加号，或者除了加号之外还会出现减号。减号表示电容器的负极应连接到外部电路中电压较低的部分。
Figure 3-11 shows the symbol for a polarized capacitor. It looks like the symbol for a nonpolarized capacitor, but a plus (+) sign appears on one side. The plus sign tells you that the positive terminal of the component should go to the more positive part of the external circuit. Occasionally, a minus (−) sign will appear on the opposite side instead of, or in addition to, the plus sign. The minus sign indicates that the negative terminal of the capacitor should go to the more negative part of the external circuit.
图 3-11 为极化电容器的符号。带加号 (+) 的一侧相对于另一侧应具有正的直流电压。
FIG. 3-11 Symbol for a polarized capacitor. The side with the plus sign (+) should carry a positive DC voltage relative to the other side.
本章中，你目前看到的电容器都是固定设计的。换句话说，这些元件的电容值是出厂时就已确定的，无法更改。但是，有些电容器的电容值是可以随意调节的。它们被称为可变电容器。一些特殊类型的可变电容器被称为微调电容器或垫片电容器。
In this chapter, all the capacitors that you’ve seen thus far have a fixed design. In other words, the components have no provision for changing the capacitance value, which the manufacturer determines at the factory. But you can adjust the values of some capacitors at will. They’re called variable capacitors. Some specialized types are known as trimmer capacitors or padder capacitors.
图 3-12显示了可变电容器最常用的符号。一条带箭头的直线斜穿过电容器。图 3-13A和3-13B显示了表示同一元件的两种替代方法。这三种符号都表示可以随意调节电容值，而无需考虑其物理结构细节。
Figure 3-12 shows the most common symbol for a variable capacitor. An arrowed line runs diagonally through it. Figures 3-13A and B show two alternative ways of denoting the same component. All three symbols indicate that you can adjust the capacitance at will, regardless of the physical construction details.
图 3-12 可变电容器的标准符号。曲线代表转子，其左侧的直线代表定子。
FIG. 3-12 Standard symbol for a variable capacitor. The curved line represents the rotor, and the straight line to its left represents the stator.
图 3-13 可变电容器的替代符号。在 A 处，定子和转子未区分；在 B 处，转子用带箭头的曲线表示。
FIG. 3-13 Alternate symbols for variable capacitors. At A, the stator is not distinguished from the rotor; at B, the rotor appears as a curved line with an arrow.
空气可变电容器（即采用空气介质的电容器）可用于调谐多种射频设备，包括天线匹配网络、发射机输出电路和老式收音机。典型的“空气可变电容器”由交错连接的极板组成，这些极板交替连接形成两个独立的触点。可旋转的极板组称为转子；固定的极板组称为定子。所有可变电容器都是无极性元件，这意味着您可以正负极性地施加外部直流电压，其性能保持不变。
An air variable capacitor (one with an air dielectric) allows you to tune many types of RF equipment including antenna matching networks, transmitter output circuits, and old-fashioned radios. A typical “air variable” has interlaced plates connected together alternately to form two distinct contact points. The rotatable set of plates is called the rotor; the stationary set of plates is called the stator. All variable capacitors are nonpolarized components, meaning that you can apply an external DC voltage either way and the performance remains the same.
有时你会看到多个可变电容器连接在一起，或者说并联。在并联可变电容器组中，两个或多个元件可以同时控制两个或多个电路。转子虽然物理上是分开的，但它们共用一个轴。图 3-14显示了该电路的原理图符号。两个可变电容器并联。这两个电容器的最小和最大电容值可能相同，但不一定相同。无论如何，它们的电容值会同步变化。当一个电容器的电容值增加时，另一个（或多个）电容器的电容值也会增加。
Sometimes you’ll see multiple variable capacitors connected together or ganged. In a set of ganged variable capacitors, two or more components can control two or more circuits at the same time. The rotors, although physically separate, all share a single shaft. Figure 3-14 shows the schematic symbol for two variable capacitors ganged together. The individual components might have identical minimum and maximum capacitance values, but not necessarily. In any case, they track together. When one capacitor increases in value, the other (or others) also increase in value.
图 3-14 两个并联可变电容器的符号。
FIG. 3-14 Symbol for two variable capacitors ganged together.
电感器和变压器
Inductors and Transformers
基本的电感器由一段盘绕的导线组成，它能为电路引入电感。电感会阻碍电流的变化。在恒定直流电下，电感器可以储存电能，但不会阻碍电流本身。电感器的物理尺寸差异很大，从微观到巨大不等，具体取决于元件的电感值及其能够承受的电流大小。
A basic inductor comprises a coiled-up length of wire that introduces inductance into a circuit. Inductance opposes changes in electric current. With constant DC, an inductor stores electrical energy but offers no opposition to the current itself. Inductors can range in physical size from microscopic to gigantic, depending on the inductance value of the component, and on the amount of current that it can handle.
电感的标准单位是亨利（符号为H）。这是一个很大的电量。大多数电感器的额定值以毫亨利（符号为mH）或微亨利（µH）为单位，其中1 mH = 0.001 H，1 µH = 0.001 mH = 0.000001 H。偶尔也会看到以纳亨利（nH）为单位的电感器，其中1 nH = 0.001 µH = 0.000000001 H。
The standard unit of inductance is called the henry (symbolized H). That’s a large electrical quantity. You’ll find most inductors rated in millihenrys (symbolized mH), where 1 mH = 0.001 H, or in microhenrys (µH), where 1 µH = 0.001 mH = 0.000001 H. Occasionally, you’ll see an inductor rated in nanohenrys (nH), where 1 nH = 0.001 µH = 0.000000001 H.
图 3-15显示了空心电感器的原理图符号。两个引线或端子用直线表示，并汇入线圈部分。空心线圈内部没有任何会影响电感的元件。有些空心线圈由硬质导线绕制而成，并依靠机械支撑。而另一些则使用塑料或陶瓷等刚性材料制成的模具来支撑线圈，使其保持固定，并在不增加电感的情况下提高元件的物理强度。
Figure 3-15 shows the schematic symbol for an air-core inductor. The two leads or terminals are designated by straight lines that merge into the coiled part. An air-core coil has nothing inside the windings that can affect the inductance. Some air-core coils are wound from stiff wire and support themselves mechanically. In other cases, a rigid form made out of plastic or ceramic material supports the coil turns, keeping them in place and enhancing the physical ruggedness of the component without making the inductance any greater.
图 3-15 空心电感器的符号。
FIG. 3-15 Symbol for an air-wound (or air-core) inductor.
图 3-16显示了抽头式空芯电感器的符号；在这种情况下，线圈沿其长度方向有两个抽头。固定电感器只有两个引线或端子（两端各一个），而抽头式电感器有三个引线或端子。或更多。当你想要对线圈进行抽头时，你需要将导线连接到线圈匝间的中间点。将末端引线或端子连接到外部电路可以获得最大电感。抽头结构允许你选择一个或多个电感值小于整个线圈电感值的点对。
Figure 3-16 shows the symbol for a tapped air-core inductor; in this case the coil has two tap points along its length. Whereas a fixed inductor has only two leads or terminals (one at either end), a tapped inductor has three or more. When you want to tap a coil, you attach conductors to turns at intermediate points. You get maximum inductance by connecting the end leads or terminals to the external circuit. A tapped arrangement lets you select one or more pairs of points having less inductance than the full coil has.
图 3-16 具有两个固定抽头的空芯电感器的符号。
FIG. 3-16 Symbol for an air-core inductor with two fixed taps.
除了抽头之外，线圈还可以配备一个滑动触点，该触点可以沿着整个绕组移动。滑动触点通过短路线直接连接到其中一个端触点，从而可以几乎连续地改变电感值（实际上，电感值会随着触点的滑动而以小幅跳跃的方式变化，每次移动一圈）。这种可变电感器可以用图 3-17A或3-17B中所示的符号来表示。
As an alternative to taps, a coil might have a sliding contact that you can move along the entire length of the windings. The sliding contact, which connects directly to one of the end contacts by means of a shorting wire, lets you vary the inductance almost continuously (actually it happens in little jumps as you slide the contact along, one turn at a time). You can portray this type of variable inductor with either of the symbols shown in Figs. 3-17A or B.
在高功率射频设备中，除了滑动抽头法之外，还有另一种改变空心线圈电感的方法。这种线圈由裸露的实心导线构成，缠绕在一个空心陶瓷圆柱体上，一根轴连接到圆柱体内的陶瓷圆盘（或一组圆盘），这样就可以带动线圈和圆柱体一起旋转。一个类似汽车轮辋（但没有轮胎）的小型轮状触点会随着线圈的旋转沿着线圈的长度移动，从而可以平滑、连续地调节“轮子”与线圈两端之间的电感。这种元件被称为滚轮电感器。您经常会在无线电天线调谐器和匹配网络中遇到滚轮电感器。图 3-18显示了其常用符号。
In equipment designed for high-power RF operation, you have an alternative to the sliding-tap method of varying the inductance of an air-core coil. The coil, consisting of solid bare wire, goes around a hollow ceramic cylindrical form, and a shaft attaches to a ceramic disk (or set of disks) inside the cylinder so that you can rotate the coil and the form together. A small wheel-like contact, resembling an automobile tire rim without the tire, travels along the length of the coil as it rotates, allowing smooth, continuous adjustment of the inductance between the “wheel” and either end. Such a component is called a roller inductor. You’ll often encounter roller inductors in radio antenna tuners and matching networks. Figure 3-18 shows a common rendition of its symbol.
图 3-17 连续可变空芯电感器的符号。A 处，箭头指向线圈符号上方；B 处，箭头斜穿过线圈符号。
FIG. 3-17 Symbols for a continuously variable air-core inductor. At A, arrow above coil symbol; at B, arrow passing diagonally through coil symbol.
图 3-18 三端滚轮电感器的符号。
FIG. 3-18 Symbol for a three-terminal roller inductor.
用于标准交流应用（例如电源滤波器中使用的60 Hz扼流圈）的电感器，可以由一段绝缘或漆包线缠绕在实心或叠片（层状）铁芯上构成。铁芯是一种铁磁性材料，它取代了空心线圈。铁磁芯增加了线圈内部的磁通密度，使其电感值比具有相同物理尺寸的空心线圈高出数千倍。图 3-19显示了具有实心或叠片铁芯的固定值电感器的标准原理图符号。它是前面讨论的基本线圈符号，外加两条贯穿其整个长度的平行直线。有时，您会看到如图 3-20所示的铁芯电感器，其中直线位于线圈匝内。
An inductor for standard AC applications, such as a 60-Hz choke for use in power-supply filters, can comprise a length of insulated or enameled wire wound around a solid or laminated (layered) iron core. The iron, a ferromagnetic material, replaces the air core. The ferromagnetic core increases the magnetic flux density inside the coil windings, making the inductance thousands of times greater than the inductance of an air-core coil having the same physical dimensions. Figure 3-19 shows the standard schematic symbol for a fixed-value inductor with a solid- or laminated-iron core. It’s the basic coil symbol discussed earlier, along with two parallel straight lines that run for its entire length. Now and then, you’ll see an iron-core inductor rendered as shown in Fig. 3-20, with the straight lines inside the coil turns.
图 3-19 实心或叠片铁芯电感器的符号。
FIG. 3-19 Symbol for an inductor with a solid- or laminated-iron core.
图 3-20 具有实心或叠片铁芯的电感器的替代符号。
FIG. 3-20 Alternate symbol for an inductor with a solid- or laminated-iron core.
有些铁芯电感器带有抽头，用于采样不同的电感值。有时你会遇到一种铁芯电感器，可以通过将铁芯推入和拉出线圈来连续改变其电感值。这类电感器的等效电路符号如图3-21A和3-21B所示。
Some iron-core inductors have taps for sampling different inductance values. Once in awhile you’ll encounter an iron-core inductor whose value you can continuously vary by pushing and pulling the core in and out of the coil. The equivalent schematic symbols for these types of inductors appear in Figs. 3-21A and B.
在高频下，实心铁芯和叠片铁芯的效率不足以用作电感器。工程师会说它们的损耗太大。在几千赫兹 (kHz) 以上的频率下，如果想要获得比空气、塑料、陶瓷或木材等非铁磁性芯材更高的电感值，就需要使用特殊的铁磁芯材料。最常用的材料是将铁粉碎成微小的碎片，每个碎片上都涂覆了一层粘性绝缘层。粉碎和绝缘完成后，这些颗粒被压缩成一种称为粉末铁芯的“固体” 。图3-22显示了三种不同类型的粉末铁芯电感器的符号。
At high frequencies, solid-iron and laminated-iron cores aren’t efficient enough to function in inductors. Engineers would say that they have too much loss. At frequencies above a few kilohertz (kHz), you’ll need a special ferromagnetic core material if you want to increase the inductance over what you can get with nonferromagnetic core materials such as air, plastic, ceramic, or wood. The most common substance for this purpose consists of iron shattered into microscopic fragments, each of which has a layer of sticky, glue-like insulation applied to it. After the fragmentation and insulation process has been completed, the particles get compressed into a “solid” object called a powdered-iron core. Figure 3-22 shows the symbols for three different types of powdered-iron-core inductors.
图 3-21 表示带抽头线圈 (A) 和带实心或叠片铁芯的可调线圈 (B) 的符号。
FIG. 3-21 Symbols for a tapped coil (A) and an adjustable coil (B) with solid- or laminated-iron cores.
图 3-22 粉末铁芯固定电感器 (A)、抽头电感器 (B) 和连续可调电感器 (C) 的符号。
FIG. 3-22 Symbols for fixed (A), tapped (B), and continuously adjustable (C) inductors with powdered-iron cores.
变压器包含两个或多个线圈，这些线圈的匝数交错排列或缠绕在同一个铁芯的不同部分上。图 3-23显示了空心变压器的符号。它看起来像两个背靠背绘制的空心线圈符号。图 3-24显示了一些铁芯变压器。A 和 B 处的变压器采用实心铁芯或叠片铁芯；C 和 D 处的变压器采用粉末冶金铁芯。
A transformer contains two or more coils with the turns interspersed or wound around different parts of a single core. Figure 3-23 shows the symbol for an air-core transformer. It looks like two air-core coil symbols drawn back-to-back. Figure 3-24 shows some transformers that have iron cores. The ones at A and B have solid- or laminated-iron cores; the ones at C and D have powdered-iron cores.
图 3-23 空心变压器的符号。
FIG. 3-23 Symbol for a transformer with an air core.
图 3-24 中，A 为实心或叠片铁芯变压器的符号；B 为带抽头绕组的实心或叠片铁芯变压器的符号；C 为粉末冶金铁芯变压器的符号；D 为粉末冶金铁芯可调变压器的符号。
FIG. 3-24 At A, symbol for a transformer with a solid- or laminated-iron core. At B, symbol for a transformer with a solid- or laminated-iron core and tapped windings. At C, symbol for a transformer with a powdered-iron core. At D, symbol for an adjustable transformer with a powdered-iron core.
在变压器中，输出电压可能等于输入电压，但通常情况下两者并不相等。升压变压器的输出电压高于输入电压，而降压变压器的输出电压低于输入电压。您可以在附录 A中找到这些变压器类型的电路图符号。
In a transformer, the output voltage might equal the input voltage, but often the voltages differ. In a step-up transformer, the output voltage is greater than the input voltage. In a step-down transformer, the output voltage is smaller than the input voltage. You’ll find schematic symbols for these transformer types in Appendix A.
开关和继电器
Switches and Relays
开关是一种可以接通或断开一条或多条电流路径的元件。图3-25显示了单刀单掷(SPST) 开关的符号。它只能接通或断开电路中的一个触点；它是一个二位器件（开/关或通/断）。当开关“接通”或“闭合”时，电流流动。当开关“断开”或“断开”时，电流停止流动。
A switch is a component that can complete or interrupt one or more current paths. Figure 3-25 shows the symbol for a single-pole/single-throw (SPST) switch. It can make or break a contact at only one point in a circuit; it’s a two-position device (on-off or make-break). With the switch “on” or “closed,” current flows. With the switch “off” or “open,” current does not flow.
图 3-25 SPST 开关的符号。
FIG. 3-25 Symbol for an SPST switch.
图 3-26是单刀双掷(SPDT) 开关的符号。极点对应于箭头线底部的触点。掷点是箭头所指的触点。您可以将极点连接到上方的掷点或下方的掷点，但不能同时连接到两者。
Figure 3-26 is the symbol for a single-pole/double-throw (SPDT) switch. The pole coincides with the point of contact at the base of the arrowed line. The throw is the contact to which the arrow points. You can connect the pole to the upper throw or the lower throw, but not to both at once.
图 3-26 SPDT 开关的符号。
FIG. 3-26 Symbol for an SPDT switch.
有些开关有两个或多个极。图 3-27中，图 A 显示了双刀单掷(DPST) 开关的符号，图 B 显示了双刀双掷(DPDT) 开关的符号。有些开关甚至包含更多元件。图 3-28所示的开关有五个极。工程师可能会称其为五刀二掷(5P2T) 开关。
Some switches have two or more poles. In Fig. 3-27, drawing A shows the symbol for a double-pole/single-throw (DPST) switch, and drawing B shows the symbol for a double-pole/double-throw (DPDT) switch. Some switches have even more elements. The one shown in Fig. 3-28 has five poles. Engineers might call it a five-pole/two-throw (5P2T) switch.
图 3-27 A 处为 DPST 开关的符号。B 处为 DPDT 开关的符号。
FIG. 3-27 At A, symbol for a DPST switch. At B, symbol for a DPDT switch.
图 3-28 五极双掷开关的符号。
FIG. 3-28 Symbol for a five-pole double-throw switch.
5P2T 器件是一种多触点开关。此类开关包括大多数至少有两个掷位的开关。例如，旋转开关可能只有一个刀位和十个掷位；图 3-29展示了这种情况。您可以称这种开关为单刀十掷(1P10T) 开关！
The 5P2T device is a multi-contact switch. This category includes most switches that have at least two throws. For instance, a rotary switch might have a single pole and ten throw positions; Fig. 3-29 shows such a scenario. You can call this thing a one-pole/ten-throw (1P10T) switch!
图 3-29 单极十掷旋转开关的符号。
FIG. 3-29 Symbol for a rotary switch with a single pole and ten throws.
有时，你会遇到成组连接的旋转开关，就像两个或多个可变电容器可以同步旋转一样。图 3-30是成组旋转开关的符号。虚线表示这些开关的动作相互同步。箭头线表示开关的拨动位置，它们同步旋转。例如，左侧开关杆停在 3 档（如图所示），右侧开关杆也停在 3 档。
Occasionally, you’ll encounter sets of rotary switches ganged together, much like two or more variable capacitors can rotate in sync with one another. Figure 3-30 is the symbol for a ganged pair of rotary switches. The dashed line tells you that the switches mimic each other’s operations. The arrowed lines indicate the throw positions, which go around in sync with each other. When the left-hand switch pole rests at, say, throw 3 (as shown here), the right-hand switch pole also rests at throw 3.
图 3-30 表示一对联动旋转开关，每个开关有一个极和十个掷。
FIG. 3-30 Symbol for a pair of ganged rotary switches, each of which has a single pole and ten throws.
图 3-31 摩尔斯电码键的符号。
FIG. 3-31 Symbol for a Morse code key.
你不可能总能在受其影响的电路或系统附近找到开关。想象一下，你想从50米外的控制点切换无线电发射器/接收器（或收发器）在两个不同天线之间的连接。天线通过同轴电缆接收信号，这些电缆传输射频电流，为了确保系统正常工作，电流必须限制在电缆内。如果电缆分支点距离控制开关的安装位置较远，可以使用一个利用电磁铁的继电器来实现远程控制。将继电器安装在电缆分支点处。然后，可以使用一段直流电线（俗称“灯线”），将继电器的电磁铁连接到控制开关。
You can’t always locate a switch near the circuit or system that it affects. Imagine that you want to switch a radio transmitter/receiver (or transceiver) between two different antennas from a control point 50 meters away. The antennas get their signals through coaxial cables that carry RF current, which must remain confined to the cables if you want the system to work properly. If the cable branch point lies far away from the place where you want to put the control switch, you can use a relay that employs an electromagnet to allow remote-control switching. You install the relay at the cable branch point. You can run a length of “lamp cord,” which carries plain DC, from the relay’s electromagnet to your control switch.
图 3-32A是单刀双掷继电器的功能图，图 3-32B显示了其原理符号。当电磁线圈中没有电流流过时，一个“弹簧条”将一个可移动的杠杆（称为衔铁）固定在一侧（在本例中为完全向上）。在这种情况下，端子 X 连接到端子 Y，但不连接到端子 Z。当线圈中有足够的直流电流时，衔铁移动到另一侧（在本例中为完全向下），此时 X 连接到 Z，而不是 Y。
Figure 3-32A is a functional drawing of an SPDT relay, and Fig. 3-32B shows its schematic symbol. A “springy strip” holds a movable lever, called the armature, to one side (which would be all the way up in this case) when no current flows through the electromagnet coil. Under these conditions, terminal X connects to terminal Y but not to Z. When sufficient DC flows in the coil, the armature moves to the other side (which would be all the way down in this case), connecting X to Z rather than to Y.
图 3-32 A 为 SPDT 继电器的功能图。B 为其原理符号。
FIG. 3-32 At A, functional drawing of an SPDT relay. At B, its schematic symbol.
常闭继电器在电磁线圈无电流时接通电路，在线圈有电流时断开电路。（这里的“常闭”指的是“线圈中无电流”。）相反，常开继电器在线圈无电流时断开电路，在线圈有电流时接通电路。图 3-32所示的继电器可以根据所选触点用作常开继电器或常闭继电器。该装置还可以切换两个不同电路之间的单条线路。
A normally closed relay completes a circuit when the electromagnet coil doesn’t carry current, and breaks the circuit when coil current flows. (“Normal” in this sense means “no current in the coil.”) In contrast, a normally open relay breaks the circuit when the coil doesn’t carry current, and completes the circuit when coil current flows. The relay portrayed in Fig. 3-32 can serve as a normally open or normally closed relay, depending on which contacts you select. The device can also switch a single line between two different circuits.
导体和电缆
Conductors and Cables
在电路图中，实线通常代表导线。大多数电路都包含许多导线。绘制复杂电路的电路图时，无论实际电路中导线是否接触，你通常都需要在屏幕或纸上绘制交叉线。
In a schematic, a solid line commonly symbolizes an electrical conductor. Most circuits contain many conductors. When you draw a schematic of a complicated circuit, you’ll often need to draw lines that cross over each other on your screen or on paper, whether the wires make contact in the real world or not.
图 3-33显示了两个在示意图中相互交叉的导线，但在实际电路中它们并不连接。这种绘图几何形状并不一定意味着它们在电路中是相通的。这意味着在实际搭建电路时，导线会在该区域彼此靠近。但在绘制电路图时，必须将一根导线画在另一根导线的上方，以避免混淆并减少电路杂乱。
Figure 3-33 shows two conductors that cross each other in a diagram, but that don’t connect in the actual circuit. This drawing geometry doesn’t necessarily mean that when you build the real circuit, the conductors come near each other in that vicinity. But when you compose the schematic, you must draw one conductor across the other to avoid confusion and minimize clutter.
图 3-33 表示原理图中交叉路径但在现实世界中不连接的导体的符号。
FIG. 3-33 Symbol for conductors that cross paths in a schematic but don’t connect in the real world.
图 3-34展示了两种表示两根导线交叉点的方法，这两个交叉点处导线确实存在电连接。在 A 图中，您将一根导线“分割”开来，使其看起来像是在两个不同的点与另一根导线接触。这种几何形状清晰地表明，在实际电路中，两根导线（“分割”的垂直导线和“完整”的水平导线）是连接的。图中的黑点表示……电接触。在图 B 中，两根导线简单地交叉，并在交叉点处画一个黑点。这个黑点告诉读者，导线在交叉处连接。图 B 的方法乍一看可能更“简洁”，但这种简洁也带来了一个问题：一些读者可能会忽略这个黑点，误以为两根导线没有连接。图 A 的方法避免了这种误解。
Figure 3-34 shows two ways of portraying a point where two wires cross and they do electrically connect there. In the rendition at A, you “split a conductor” so it seems to contact the other one at two different points. This geometry makes it clear that the two conductors (the “split” vertical one and the “solid” horizontal one) connect in the real circuit. Black dots portray electrical contact. In the drawing at B, the two conductors simply cross each other, and you draw a single black dot at the junction. The dot tells your readers that the conductors connect where they cross. The method shown at B might look “cleaner” at first glance, but with this neatness comes a problem: Some readers might overlook the black dot and think that the two conductors do not connect. The method at A avoids such misunderstandings.
图 3-34 中，A 为原理图中交叉路径且在实际应用中连接的导体的优选符号。B 为相同情况下的替代符号。
FIG. 3-34 At A, preferred symbol for conductors that cross paths in a schematic and actually connect in the real world. At B, alternative symbol for the same scenario.
在一些较老的电路图中，你会看到如图 3-35所示的交叉导线。这些导线在实际电路中并不连接。其中一根导线有一个半环或“跳线”，使其看起来像是“跳过”了另一根导线。这种技巧（在我看来，它本不应该被淘汰）消除了所有关于实际导线是否在交叉点连接的疑虑。
In some older schematics you’ll see crossed wires shown as in Fig. 3-35. These wires don’t connect in the real circuit. One of the lines has a half loop or “jog” that makes it seem to “jump” over the other line. That trick (which should never have gone out of style, in my opinion) eliminates all doubt as to whether or not the actual wires connect where the lines cross.
图 3-35 示意图中交叉路径但现实世界中不连接的导体的古老（但清晰）表示。
FIG. 3-35 Archaic (but clear) representation of conductors that cross paths in a schematic but don’t connect in the real world.
电缆由一个或多个导体组成，这些导体位于同一绝缘护套内。在许多情况下，非屏蔽电缆在原理图中不会明确标示，而是用两条或多条平行线表示多个导体。屏蔽电缆除了导体之外，还需要额外的符号。图 3-36 A和B显示了屏蔽电缆的符号。这些符号用于表示同轴电缆，同轴电缆由一根称为中心导体的导线和包裹其周围的圆柱形导管状导电屏蔽层组成。在图 A 处，屏蔽层未连接到任何特定设备；在图 B 处，屏蔽层连接到地线。绝缘层（称为介质层）使中心导体与屏蔽层隔离。在大多数同轴电缆中，介质材料由固体或泡沫聚乙烯构成。
A cable has one or more conductors inside a single insulating jacket. In many cases, unshielded cables are not specifically indicated in a schematic drawing, but appear as two or more lines that run parallel to indicate multiple conductors. Shielded cables require additional symbology along with the conductors. Figures 3-36 A and B show symbols for shielded cable. You’ll see these symbols drawn to indicate coaxial cable, which comprises a single wire called the center conductor surrounded by a cylindrical, conduit-like conductive shield. At A, the shield does not connect to anything in particular, but at B, the shield connects to an earth ground. An insulating layer, called the dielectric, keeps the center conductor isolated from the shield. In most coaxial cables, the dielectric material consists of solid or foamed polyethylene.
图 3-36 中，A 为非接地屏蔽层同轴电缆的符号，B 为接地屏蔽层同轴电缆的符号。
FIG. 3-36 At A, symbol for coaxial cable with an ungrounded shield. At B, symbol for coaxial cable with an earth-grounded shield.
图 3-37 带底盘接地屏蔽层的同轴电缆符号。
FIG. 3-37 Symbol for coaxial cable with a chassis-grounded shield.
在某些电缆中，单层屏蔽层包裹着两根或多根导体。图 3-38显示了双芯屏蔽电缆的符号，其屏蔽层接地。该符号与单芯同轴电缆的符号类似，只是多了一根内导体。如果屏蔽电缆的内导体超过两根，则穿过符号椭圆部分的平行直线数量表示屏蔽层内的导体数量。例如，如果图 3-38中的电缆有五根内导体，则符号的椭圆部分将有五条水平线穿过。
In some cables, a single shield surrounds two or more conductors. Figure 3-38 shows the symbol for two-conductor shielded cable whose shield goes to a chassis ground. This symbol looks like the one for single-conductor coaxial cable, except that it has an extra inner conductor. If shielded cable has more than two inner conductors, then the number of straight, parallel lines going through the elliptical part of the symbol tells you how many conductors run inside the shield. For example, if the cable in Fig. 3-38 had five inner conductors, then five horizontal lines would pass through the elliptical part of the symbol.
图 3-38 带底盘接地屏蔽层的双芯电缆符号。
FIG. 3-38 Symbol for two-conductor cable with a chassis-grounded shield.
二极管和晶体管
Diodes and Transistors
图 3-39是半导体二极管的常用符号。箭头和垂直线表示二极管的各个部分，左右两侧的水平线表示引脚。符号中带箭头的部分对应于阳极，箭头尖端的短直线对应于阴极。
Figure 3-39 is the common symbol for a semiconductor diode. An arrow and a vertical line indicate parts of the diode, and the horizontal lines to the left and right indicate the leads. The arrowed part of the symbol corresponds to the anode, and the short, straight line at the arrow’s tip corresponds to the cathode.
图 3-39 通用半导体二极管的符号。
FIG. 3-39 Symbol for a general-purpose semiconductor diode.
理想二极管在电子逆向移动时导通，此时阳极相对于阴极具有正电压。工程师称这种状态为正向偏置。理想二极管在阴极相对于阳极具有正电压时不导通。工程师称这种状态为反向偏置。但当然，在这个并不完美的世界里，没有什么是“理想”的。
An ideal diode conducts current when electrons move against the arrow so the anode has a positive voltage with respect to the cathode. Engineers call that condition forward bias. The ideal diode does not conduct when the cathode has a positive voltage with respect to the anode. Engineers call that a state of reverse bias. But of course, nothing is “ideal” in this imperfect universe.
图 3-40展示了三种特殊类型的二极管。图 A 为变容二极管的符号，当施加波动的反向偏置电压时，它可以作为可变电容器工作。图 B 为齐纳二极管的符号，它可以用作交流转直流电源中的稳压器。图 C 为耿氏二极管的符号，它可以产生或放大极高频和微波频率的无线电信号。
Figure 3-40 portrays three specialized diode types. Drawing A shows the symbol for a varactor diode, which can act as a variable capacitor when you apply a fluctuating reverse-bias voltage. Drawing B shows the symbol for a Zener diode, which can serve as a voltage regulator in a power supply that converts AC to DC. Drawing C shows the symbol for a Gunn diode, which can generate or amplify radio signals at extremely high and microwave frequencies.
图 3-40 变容二极管 (A)、齐纳二极管 (B) 和耿氏二极管 (C) 的符号。
FIG. 3-40 Symbols for a varactor diode (A), a Zener diode (B), and a Gunn diode (C).
硅控整流器(SCR) 实际上是一种带有额外元件和端子的半导体二极管。您可以在图 3-41中看到它的符号。在 SCR 的表示中，二极管符号通常（但不总是）被一个圆圈或椭圆包围，控制元件（称为栅极）则表示为从箭头尖端向外延伸的对角线。在所有情况下，箭头都表示阳极，箭头尖端的垂直线表示阴极。
A silicon-controlled rectifier (SCR) is, in effect, a semiconductor diode with an extra element and terminal. You’ll see its symbol in Fig. 3-41. In the SCR representation, a circle or ellipse often (but not always) surrounds the diode symbol, and the control element, called the gate, appears as a diagonal line that runs outward from the tip of the arrow. In all cases, the arrow denotes the anode, and the vertical line at the arrow’s tip denotes the cathode.
图 3-41 硅控整流器 (SCR) 的符号。
FIG. 3-41 Symbol for a silicon-controlled rectifier (SCR).
图 3-42显示了双极型晶体管的电路符号。A 处为 PNP 型晶体管， B 处为NPN 型晶体管。在 PNP 型晶体管符号中，箭头指向基极，远离发射极。在 NPN 型晶体管符号中，箭头指向发射极，远离基极。有些工程师会省略包围基极、发射极和集电极的圆圈。
Figure 3-42 shows schematic symbols for bipolar transistors. A so-called PNP transistor appears at A, and an NPN transistor appears at B. In the PNP symbol, the arrow points away from the emitter and toward the base. In the NPN symbol, the arrow points away from the base and toward the emitter. Some engineers leave out the circle that surrounds the combined base, emitter, and collector symbols.
图 3-42 PNP 双极晶体管 (A) 和 NPN 双极晶体管 (B) 的符号。
FIG. 3-42 Symbols for a PNP bipolar transistor (A) and an NPN bipolar transistor (B).
图 3-43 中，A 为 N 沟道 JFET 的符号，B 为 P 沟道 JFET 的符号，C 为 N 沟道耗尽型 MOSFET 的符号，D 为 P 沟道耗尽型 MOSFET 的符号。
FIG. 3-43 At A, symbol for an N-channel JFET. At B, symbol for a P-channel JFET. At C, symbol for an N-channel depletion-mode MOSFET. At D, symbol for a P-channel depletion-mode MOSFET.
除了双极型晶体管之外，你还会遇到其他类型的晶体管。图 3-43显示了其中四种器件的符号，如下所示：
Along with the bipolar variety, you’ll encounter other types of transistors. Figure 3-43 shows the symbols for four of these devices, as follows:
• 在 A 处，您可以看到一个N 沟道结型场效应晶体管(JFET)。
• At A, you see an N-channel junction field-effect transistor (JFET).
• 在 B 处，您可以看到一个P 沟道 JFET。
• At B, you see a P-channel JFET.
• 在 C 处，您可以看到一个N 沟道耗尽型金属氧化物半导体场效应晶体管(MOSFET)。
• At C, you see an N-channel depletion-mode metal-oxide-semiconductor field-effect transistor (MOSFET).
• 在 D 处，您可以看到一个P 沟道耗尽型 MOSFET。
• At D, you see a P-channel depletion-mode MOSFET.
当源极和栅极之间没有施加偏置电压时，耗尽型 MOSFET 的沟道是开路（导通）；当施加偏置电压时，沟道会收缩，最终完全闭合，此时器件处于夹断状态。有时在电子电路中还会看到另一种类型的 MOSFET：增强型MOSFET。增强型器件的沟道在源极和栅极之间没有施加偏置电压时处于夹断状态。随着偏置电压的增加，沟道会逐渐打开。图 3-44A是N 沟道增强型 MOSFET的符号。图 3-44B是P 沟道增强型 MOSFET的符号。
A depletion-mode MOSFET has an open (conducting) channel when you don’t apply any bias voltage between the source and the gate; when you do impose a bias voltage, the channel constricts and eventually closes off altogether. Then you have a state of pinchoff. Sometimes you’ll see another type of MOSFET in electronic circuits: the enhancement-mode MOSFET. An enhancement-mode device has a pinched-off channel unless you apply a bias voltage between the source and the gate. Then the channel opens wider and wider as you increase the bias voltage. Figure 3-44A is the symbol for an N-channel enhancement-mode MOSFET. Figure 3-44B shows the symbol for a P-channel enhancement-mode MOSFET.
图 3-44 A 为 N 沟道增强型 MOSFET 的符号。B 为 P 沟道增强型 MOSFET 的符号。
FIG. 3-44 At A, symbol for an N-channel enhancement-mode MOSFET. At B, symbol for a P-channel enhancement-mode MOSFET.
运算放大器
Operational Amplifiers
运算放大器（简称运放）是一种特殊的集成电路（IC），它由双极型晶体管、电阻器、二极管和/或电容器组成，所有这些元件连接在一起以产生或修改信号。（除了运放之外，还有许多其他类型的集成电路。图 3-45显示了集成电路的通用符号。）有时，您会在一个集成电路封装中发现两个或多个运放；例如，您可能会遇到双运放或四运放。
An operational amplifier or op amp is a specialized integrated circuit (IC) that comprises bipolar transistors, resistors, diodes, and/or capacitors, all connected together to produce or modify a signal. (Myriad types of ICs exist besides the op amp. Figure 3-45 shows the general symbol for an IC.) Sometimes you’ll find two or more op amps in a single IC package; for example, you might encounter a dual op amp or a quad op amp.
图 3-45 集成电路 (IC) 的通用符号。
FIG. 3-45 Generic symbol for an integrated circuit (IC).
图 3-46是运算放大器的原理图符号。该器件有两个输入端，一个是同相输入端，用加号 (+) 表示；另一个是反相输入端，用减号 (−) 表示。当信号输入到同相输入端时，输出波形与输入波形相位一致（“正向”）。当信号输入到反相输入端时，输出波形与输入波形相位相反（“倒向”）。该器件有两个电源连接，一个用于内部双极型晶体管的发射极 (V <sub> e</sub> )，另一个用于集电极 (V <sub>cc </sub> )。
Figure 3-46 is the schematic symbol for an op amp. The device has two inputs, one non-inverting, indicated by a plus (+) sign, and the other inverting, as shown by the minus (−) sign. When a signal enters the non-inverting input, the output wave emerges in phase coincidence (“right-side-up”) with respect to the the input wave. When a signal enters the inverting input, the output wave appears in phase opposition (“upside-down”) with respect to the input wave. The device has two power-supply connections, one for the emitters of the internal bipolar transistors (Vee) and one for the collectors (Vcc).
图 3-46 运算放大器（运放）的符号。
FIG. 3-46 Symbol for an operational amplifier (op amp).
当信号输入到任一输入端进行放大时，可以在输出端和反相输入端之间连接一个电阻，以产生负反馈，从而降低或控制增益。随着电阻值的减小，由于负反馈增强，增益也会降低。这种情况称为闭环配置。
When a signal comes into either input for amplification, you can place a resistor between the output and the inverting input to cause negative feedback that reduces or controls the gain. As you reduce the value of the resistor, the gain decreases because the negative feedback increases. This state of affairs is called the closed-loop configuration.
如果在运算放大器的反相反馈回路中安装电阻-电容(RC) 组合，则增益取决于输入信号的频率。使用特定的电阻和电容值，可以制作一个频率敏感滤波器，该滤波器可提供如图 3-47所示的四种不同特性：
If you install a resistance-capacitance (RC) combination in the inverting-feedback loop of an op amp, the gain depends on the frequency of the signal that enters the device. Using specific values of resistance and capacitance, you can make a frequency-sensitive filter that provides any of four different characteristics as shown in Fig. 3-47:
图 3-47 增益与频率响应曲线。A 点为低通滤波器；B 点为高通滤波器；C 点为谐振峰；D 点为谐振陷波滤波器。
FIG. 3-47 Gain-versus-frequency response curves. At A, lowpass; at B, highpass; at C, resonant peak; at D, resonant notch.
•有利于低频的低通响应（A）。
• A lowpass response that favors low frequencies (A).
•有利于高频的高通响应（B）。
• A highpass response that favors high frequencies (B).
•在单一频率 (C) 处具有最大增益的共振峰。
• A resonant peak with maximum gain at a single frequency (C).
•在单一频率 (D) 处具有最小增益的谐振陷波。
• A resonant notch with minimum gain at a single frequency (D).
电子管
Electron Tubes
虽然电子管（通常简称为电子管）不像几十年前那样常见，但许多电路和系统仍然使用它们。要表示电子管，应该先画一个圆圈，然后在圆圈内添加必要的符号来表示电子管的类型。图 3-48显示了各种内部电子管元件的符号。
Although you won’t encounter electron tubes (often simply called tubes) as frequently as you would have a few decades ago, plenty of circuits and systems still use them. When you want to create the symbol for a tube, you should draw a circle and then add the necessary symbols inside the circle to portray the type of tube involved. Figure 3-48 shows the symbols for various internal tube elements.
图 3-48 电子管元件及其特性的符号。A：灯丝或直接加热阴极。B：间接加热阴极。C：冷阴极。D：光电阴极。E：栅极。F：阳极（阳极板）。G：偏转板。H：聚焦板。I：真空管外壳。J：充气管外壳。
FIG. 3-48 Symbols for electron-tube elements and characteristics. A: Filament or directly heated cathode. B: Indirectly heated cathode. C: Cold cathode. D: Photocathode. E: Grid. F: Anode (plate). G: Beam-deflection plate. H: Beam-focusing plates. I: Envelope (enclosure) for a vacuum tube. J: Envelope for a gas-filled tube.
图 3-49显示了二极管真空管的示意图符号。这种双元件包含阳极（也称阳极板）和阴极。与半导体二极管类似，当器件导通时，阳极通常比阴极具有更高的正电压。当阳极比阴极具有更低的负电压时，器件通常不导通。阴极发射电子，这些电子穿过真空到达阳极。一根热丝灯丝（类似于微型白炽灯泡）加热阴极，以帮助驱动电子。为了简化图示，图 3-49中省略了灯丝，这在真空管符号中是一种常见的做法，尤其是在灯丝和阴极物理分离的情况下，这种结构称为间接加热阴极。
Figure 3-49 shows the schematic symbol for a diode vacuum tube. This two-element component contains an anode (also called a plate) and a cathode. As with a semiconductor diode, the anode normally carries a more positive voltage than the cathode when the device conducts current. When the anode has a more negative voltage than the cathode, the device generally does not conduct. The cathode emits electrons that travel through the vacuum to the anode. A hot-wire filament, something like a miniature incandescent bulb, heats the cathode to help drive electrons from it. In Fig. 3-49, the filament has been omitted for simplicity, a common practice in vacuum tube symbols when the filament and cathode are physically separate, an arrangement known as an indirectly heated cathode.
图 3-49 为间接加热阴极二极管真空管的示意图。虽然图中存在灯丝，但为了简化电路，通常省略灯丝。
FIG. 3-49 Schematic symbol for a diode vacuum tube with an indirectly heated cathode. Although a filament exists, it’s often omitted to reduce clutter.
图 3-50展示了两种三极管真空管，其元件与前面讨论的二极管相同，只是增加了一条虚线来表示栅极。但图 3-50A与图 3-49之间还存在另一个区别。仔细观察阴极。图 3-50A所示的电子管采用直接加热式阴极，其中灯丝和阴极是同一个物理实体！将负极阴极电压直接施加到灯丝上。图 3-50B显示的是间接加热式阴极三极管的符号。在这种情况下，灯丝位于阴极内部，阴极实际上是一个沿电子管中心垂直轴线延伸并环绕灯丝的金属圆柱体。
Figure 3-50 shows two versions of a triode vacuum tube, which consists of the same elements as the diode previously discussed, with the addition of a dashed line to indicate the grid. But another difference exists in Fig. 3-50A compared with Fig. 3-49. Look closely at the cathode. The tube shown in Fig. 3-50A has a directly heated cathode, in which the filament and the cathode are the same physical object! You apply the negative cathode voltage directly to the filament. Figure 3-50B shows the symbol for a triode tube with an indirectly heated cathode. In this case the filament resides inside the cathode, which physically takes the form of a metal cylinder running along the central vertical axis of the tube, surrounding the filament.
图 3-50 直接加热阴极 (A) 和间接加热阴极 (B) 三极管的符号。
FIG. 3-50 Symbols for triode tubes with a directly heated cathode (A) and an indirectly heated cathode (B).
四极真空管有两个栅极，因此需要如图 3-51 A和B所示，画一条额外的虚线。在四极管中，靠近阳极的上栅极称为帘栅极（或简称帘栅极）。图 3-52显示了五极管的符号，五极管有三个栅极，总共有五个元件。在五极管中，中间的栅极是帘栅极，顶部的栅极称为抑制栅极（或简称抑制栅极）。
Tetrode vacuum tubes have two grids, so you must draw an additional dashed line as shown in Figs. 3-51 A and B. In the tetrode, the upper grid, closer to the anode, is called the screen grid (or simply the screen). Figure 3-52 shows symbols for a pentode tube, which has three grids and a total of five elements. In the pentode, the middle grid is the screen, and the top grid is called the suppressor grid (or simply the suppressor).
图 3-51 直接加热阴极 (A) 和间接加热阴极 (B) 四极管的符号。
FIG. 3-51 Symbols for tetrode tubes with a directly heated cathode (A) and an indirectly heated cathode (B).
图 3-52 直接加热阴极 (A) 和间接加热阴极 (B) 五极管的符号。
FIG. 3-52 Symbols for pentode tubes with a directly heated cathode (A) and an indirectly heated cathode (B).
图 3-51A和3-52A描绘了直接加热阴极的电子管，而图 3-51B和3-52B则描绘了间接加热阴极的电子管。
Figures 3-51A and 3-52A portray tubes with directly heated cathodes, while Figs. 3-51B and 3-52B symbolize tubes with indirectly heated cathodes.
有些电子管由两组独立的电极组成，封装在同一个管体中。这些元件被称为双极管。如果两组电极完全相同，则整个元件被称为双二极管、双三极管、双四极管或双五极管。图 3-53显示了间接加热阴极双三极管真空管的电路符号。
Some tubes consist of two separate, independent sets of electrodes housed in a single envelope. These components are called dual tubes. If the two sets of electrodes are identical, the entire component is called a dual diode, dual triode, dual tetrode, or dual pentode. Figure 3-53 shows the schematic symbol for a dual triode vacuum tube with indirectly heated cathodes.
图 3-53 间接加热阴极双三极管的符号。
FIG. 3-53 Symbol for a dual triode tube with indirectly heated cathodes.
在老式收音机和电视接收机中，有时会发现四栅极或五栅极的电子管。这些电子管分别有六个和七个元件，被称为六极管和七极管。它们用于混频，混频是将两个不同频率的射频信号混合，产生和频和差频的新信号的过程。图 3-54A显示了六极管的电路符号；图 3-54B显示了七极管的电路符号。一些工程师将七极管称为五栅极转换器。
In old radio and television receivers, you’ll sometimes find tubes with four or five grids. These tubes have six and seven elements, respectively, and are called a hexode and a heptode. They work for mixing, a process in which two RF signals having different frequencies combine to produce new signals at the sum and difference frequencies. Figure 3-54A shows the schematic symbol for a hexode; Fig. 3-54B shows the symbol for a heptode. Some engineers call the heptode a pentagrid converter.
图 3-54 中，A 为六极管符号，B 为七极管（也称五栅转换器）符号。两种符号均表示间接加热阴极的电子管。
FIG. 3-54 At A, symbol for a hexode tube. At B, symbol for a heptode tube, also called a pentagrid converter. Both symbols show tubes with indirectly heated cathodes.
电化学电池和蓄电池
Electrochemical Cells and Batteries
您经常会看到电池或电芯被用作电路或系统的电源。图 3-55显示了单个电化学电池的原理图符号，例如手电筒中使用的那种电池。大多数此类电池产生约 1.5 V 直流电压。
You’ll often see a cell or battery employed as the power source for a circuit or system. Figure 3-55 shows the schematic symbol for a single electrochemical cell, such as the sort that you’ll find in a flashlight. Most such cells produce approximately 1.5 V DC.
图 3-55 单个电化学电池的符号。
FIG. 3-55 Symbol for a single electrochemical cell.
具有较高电压输出的电化学电池由多个串联的电池组成（负极到正极串联成链或串）；多节电池的符号考虑了这种设计，如图3-56所示。
Electrochemical batteries with higher voltage outputs comprise multiple cells connected in series (negative-to-positive in a chain or string); the symbol for a multicell battery takes this design into account as shown in Fig. 3-56.
图 3-56 自包含多节电化学电池的符号。
FIG. 3-56 Symmbol for a self-contained multicell electrochemical battery.
如果电路需要一个由两个或多个串联的独立单节电池组成的多节电池组，您可以分别绘制每个单节电池的符号，并在它们之间用导线符号连接。图 3-57显示了一个包含三个单节电池的示例。
If a circuit calls for a multicell battery in the form of two or more discrete single cells in series, you can draw the single-cell symbols individually with wire conductor symbols between them. Figure 3-57 shows an example with three cells.
图 3-57 表示三个串联的单电化学电池组成电池的符号。
FIG. 3-57 Symbol for three single electrochemical cells connected in series to form a battery.
标准做法要求电池或电芯的符号必须与极性标志相对应。遗憾的是，有些人会忽略这个细节。这样一来，在查看电路图时，就不得不通过仔细观察电路的其他部分来推断电池或电芯的极性。（较长的末端线通常连接正极，但并非总是如此。）
Standard practice calls for polarity signs to go with the symbols for cells or batteries. Unfortunately, some people neglect this detail. Then when you look at the schematic, you’ll have to infer the cell or battery polarity by scrutinizing the rest of the circuit. (The longer end line usually goes with the positive terminal, but not always.)
逻辑门
Logic Gates
所有数字电子设备都使用开关来执行特定的逻辑运算。这些开关被称为逻辑门，可以有一个或多个输入和一个输出。逻辑门只有两种状态，分别用数字 0 和 1 表示。在大多数情况下，0 代表低电平状态，1 代表高电平状态。
All digital electronic devices employ switches that perform specific logical operations. These switches, called logic gates, can have from one to several inputs and a single output. Logic devices have two states, represented by the digits 0 and 1. In most cases, 0 represents the low state and 1 represents the high state.
逻辑反相器，也称为非门，有一个输入和一个输出。它反转输入的状态。如果输入为 1，则输出为 0；如果输入为 0，则输出为 1。图 3-58A显示了它的符号。
• A logical inverter, also called a NOT gate, has one input and one output. It reverses, or inverts, the state of the input. If the input equals 1, then the output equals 0. If the input equals 0, then the output equals 1. Figure 3-58A shows its symbol.
•或门可以有两个或多个输入（尽管通常只有两个）。如果两个或所有输入都为 0，则输出为 0。如果任何一个输入为 1，则输出为 1。数学家称这种门执行的是包含或运算。图 3-58B显示了它的符号。
• An OR gate can have two or more inputs (although it usually has only two). If both, or all, of the inputs equal 0, then the output equals 0. If any input equals 1, then the output equals 1. Mathematicians would say that such a gate performs an inclusive-OR operation. Figure 3-58B shows its symbol.
•与门可以有两个或多个输入（尽管通常只有两个）。如果两个或所有输入都等于 1，则输出等于 1。如果任何一个输入等于 0，则输出等于 0。图 3-58C显示了它的符号。
• An AND gate can have two or more inputs (although it usually has only two). If both, or all, of the inputs equal 1, then the output equals 1. If any input equals 0, then the output equals 0. Figure 3-58C shows its symbol.
• 一个或门后面可以接一个非门。这种组合构成了一个非或门，更常被称为或非门。如果两个或所有输入都为 0，则输出为 1。如果任何一个输入为 1，则输出为 0。图 3-58D显示了它的符号。
• An OR gate can be followed by a NOT gate. This combination gives you a NOT-OR gate, more often called a NOR gate. If both, or all, of the inputs equal 0, then the output equals 1. If any inputs equals 1, then the output equals 0. Figure 3-58D shows its symbol.
图 3-58 逻辑反相器或非门 (A)、或门 (B)、与门 (C)、或非门 (D)、与非门 (E) 和异或门 (F) 的符号。
FIG. 3-58 Symbols for a logical inverter or NOT gate (A), an OR gate (B), an AND gate (C), a NOR gate (D), a NAND gate (E), and an XOR gate (F).
• 与门后可以接一个非门。这种组合构成一个非与门，更常被称为与非门。如果两个或所有输入都等于 1，则输出等于 0。如果任何一个输入等于 0，则输出等于 1。图 3-58E显示了它的符号。
• An AND gate can be followed by a NOT gate. This combination gives you a NOT-AND gate, more often called a NAND gate. If both, or all, of the inputs equal 1, then the output equals 0. If any input equals 0, then the output equals 1. Figure 3-58E shows its symbol.
异或门（也称XOR 门）有两个输入和一个输出。如果两个输入状态相同（均为 1 或均为 0），则输出为 0；如果两个输入状态不同，则输出为 1。数学家称这种门执行异或运算。图 3-58F显示了它的符号。
• An exclusive OR gate, also called an XOR gate, has two inputs and one output. If the two inputs have the same state (both 1 or both 0), then the output equals 0. If the two inputs have different states, then the output equals 1. Mathematicians would say that such a gate performs the exclusive-OR operation. Figure 3-58F shows its symbol.
表 3-1 逻辑门及其特性。
TABLE 3-1 Logic gates and their characteristics.
概括
Summary
本章介绍了电路图中大部分常见的符号，但还有许多符号并未在此列出。附录 A中提供了完整的电路图符号表。您将看到插孔和插头、压电晶体、灯、麦克风、仪表、天线以及许多其他元件的符号。
This chapter identifies most of the symbols that you’ll see in schematics, but plenty of symbols exist that are not included here. You’ll find a comprehensive table of schematic symbols in Appendix A. You’ll see symbols for jacks and plugs, piezoelectric crystals, lamps, microphones, meters, antennas, and many other components.
你觉得记住所有这些符号会很困难吗？别担心，随着时间的推移，你会逐渐熟悉它们。读完本章后，先看看一些简单的示意图。遇到不认识的符号时，请参考附录A。几个小时后，你就可以开始研究更复杂的示意图了，当然，你仍然需要参考那些不认识的符号。经过几个周末的练习，你就能不假思索地认出大多数符号了。
Do you expect to have a difficult time memorizing all these symbols? Well, don’t worry; you’ll get to know them over time. Look at some simple schematics after you’ve read this chapter. Refer to Appendix A whenever you see a symbol that you can’t identify. Within a few hours you’ll want to move on to more complex schematics, again referencing the unknown symbols. After a few weekends of practice, you’ll recognize most symbols without even thinking.
在电气和电子领域，大多数符号都源自它们所代表的元件结构。电路符号通常成组出现，每组符号之间都存在某种关联。例如，你会遇到许多不同类型的晶体管，但它们看起来都有些相似。二极管、电阻器、电容器、电感器、变压器、仪表、灯泡以及大多数其他电子元件的符号也遵循同样的规律。大多数符号都遵循这些规律，但并非全部。有一些“特立独行”的符号，它们似乎违背了常理。对于这些符号，你只能记住它们，然后挠挠头，最后苦笑。
In electricity and electronics, most symbols derive from the structures of the components they represent. Schematic symbols often appear in groups, each of which bears some relationship to the others. For example, you’ll encounter many different types of transistors, but they all look somewhat alike. The same rule applies to the symbols for diodes, resistors, capacitors, inductors, transformers, meters, lamps, and most other electronic components. Most, but not all. A few “renegade” symbols exist that defy reason. All you can do with these things is memorize them, scratch your head, and laugh.
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4
简单电路
Simple Circuits
在教授电路图的人群中，主要有两种观点。一些导师认为应该先学会读懂电路图再学习绘制电路图，而另一些导师则坚持认为应该边学边画。两种观点各有优点，让我们取长补短！你可以先从学习（或者说是记忆）基本的元件符号入手，然后尝试阅读所有你看到的电路图。当你开始觉得枯燥乏味时，就可以尝试自己绘制电路图了。
Among people who teach about schematics, two schools of thought prevail. Some mentors say that you should learn to read schematics before you learn to draw them. Others insist that you should learn to read them while you learn to draw them. Either view has its merits, so let’s take advantage of them both! You can start by learning (okay, memorizing) the basic component symbols. Then you can try to read all the schematics that you see. When this business begins to bore you, then you can draw your own schematics.
入门
Getting Started
本章将介绍简单的电路图，包括图示和原理图。你可以先拼凑出一个电路，然后画出这个“怪物”的原理图。偶尔，这种方法一次就能成功，但这种好运并不常见。大多数工程师和发明家都会先画出原理图，然后再根据原理图搭建和测试实际电路。
This chapter deals with simple circuit diagrams in pictorial and schematic form. You can cobble a circuit together and then draw a schematic of the “beast” that you’ve created. Once in awhile, this approach works on the first try, but such good luck doesn’t strike very often. Most engineers and inventors draw a schematic to start, and then build and test the actual circuit on the basis of the diagram.
如果设计是全新的或实验性的，那么第一个版本（称为原型）中很可能存在一些缺陷，需要对各种元件进行删除、添加或替换。每次修改测试电路时，都可以记录结果并相应地修改原理图。最终，最终修正后的原理图将体现设计理论、实时测试和“微调”的结果。
If the design is new or experimental, some bugs (flaws) will probably exist in the first version, called the prototype, necessitating various component deletions, additions, or substitutions. Every time you modify the test circuit, you can note the results and change the schematic accordingly. In the end, the finished and corrected schematic will reflect the result of design theory, real-time testing, and “tweaking.”
图 4-1展示了一个简单的电路，你可能曾经搭建过类似的电路。它本质上就是一个没有外壳和开关的手电筒。该装置由一个电化学电池和一个白炽灯泡组成。图中还显示了连接灯泡和电池的导线。电流从电池流出，经过灯泡，再流回电池，如此循环往复，直到电池耗尽或灯泡烧毁。
Figure 4-1 shows a simple circuit that you’ve likely built at one time or another. Basically, it’s a flashlight without the external case and switch. The device consists of a single electrochemical cell and an incandescent light bulb. This pictorial also shows the conductors, which attach to the bulb and the cell. The conductors carry current out of the cell, through the bulb, back through the cell, through the bulb again, around and around until the cell dies or the bulb burns out.
图 4-1 手电筒电路示意图，包括电化学电池、导线和白炽灯泡。
FIG. 4-1 Pictorial drawing of a flashlight circuit comprising an electrochemical cell, some wire, and an incandescent bulb.
要绘制图 4-1所示手电筒的原理图，您必须了解三个符号。它们分别代表电池、导线和灯泡（图 4-2）。一旦您了解了这些符号，就可以根据图中电路的形状绘制原理图。
In order to draw a schematic of the flashlight illustrated in Fig. 4-1, you must know three symbols. They represent the cell, the conductors, and the bulb (Fig. 4-2). Once you know the symbols, you can draw a schematic based on the appearance of the circuit in the pictorial.
图 4-2 电化学电池 (A)、导线等电导体 (B) 和白炽灯泡 (C) 的示意图符号。
FIG. 4-2 Schematic symbols for an electrochemical cell (A), an electrical conductor such as wire (B), and an incandescent bulb (C).
首先画出电池符号。你可以把电池想象成电路的“心脏”，因为它负责将电子输送到电路的各个部分。接下来是灯泡符号，你可以把它画在电池符号附近的任意位置。在这个例子中，你应该尽量按照图示中的位置来排列电路符号，也就是说，灯泡符号应该放在电池符号的上方。
Start by drawing the cell symbol. You can think of the cell as the “heart” of the circuit because it “pumps” electrons through everything. Next comes the symbol for the bulb, which you can draw at any point near the cell symbol. Using this example, you should try to arrange the schematic symbols in the same relative positions as they appear in the pictorial, so you’d place the bulb symbol above the cell symbol.
现在你已经画出了两个主要符号，可以使用导体符号（黑色实线）将它们连接起来。请注意，图示中显示了两个导体。因此，原理图也显示了两个导体。图 4-3显示了完整的原理图，它是图 4-1的符号等效图。
Now that you’ve drawn the two major symbols, you can use conductor symbols (solid black lines) to connect them together. Notice that the pictorial shows two conductors. Therefore, the schematic diagram also shows two conductors. Figure 4-3 shows the completed schematic, the symbolic equivalent of Fig. 4-1.
图 4-3 单节电池手电筒示意图。
FIG. 4-3 Schematic diagram of a single-cell flashlight.
图 4-4显示了图 4-3所示单节电池手电筒的两种替代原理图。这三个图（图 4-3中的图和图 4-4中的两个图）都表示同一个电路，但由于符号在页面上的相对位置不同，它们看起来有所不同。
Figure 4-4 shows two alternative schematics of the single-cell flashlight diagrammed in Fig. 4-3. All three of these diagrams (the one in Fig. 4-3 and the two in Fig. 4-4) represent the same circuit, but they look different because of the relative positions of the symbols on the page.
图 4-4 手电筒原理图的替代布置方案。A 方案中，电池位于右侧，灯泡位于左侧；B 方案中，电池和灯泡均位于上方。
FIG. 4-4 Alternative arrangements for the flashlight schematic. At A, cell on the right and bulb on the left; at B, cell and bulb both on the top.
图 4-5显示了一个带有开关和两节电池的手电筒。仔细观察这张图，你会发现任何电路原理图都必须包含两个电池符号、导线、灯泡和开关。图 4-6显示了绘制该手电筒完整电路原理图所需的符号。同样，你应该按照图中元件出现的顺序绘制这些符号。图 4-7显示了绘制结果。两个电池符号分别绘制，串联连接，并分别标明极性。在串联连接中，一节电池的正极连接到另一节电池的负极。你需要使用两根导线连接电池的正负极，第三根导线连接开关和灯泡。你可能还需要第四根导线将两节电池连接起来形成电池组（除非电池直接紧贴在一起，这是市售手电筒的常见结构）。图 4-7显示开关处于“关闭”位置。
Figure 4-5 shows a flashlight with a switch and two cells. When you examine this pictorial, you’ll see that any schematic rendition must have two cell symbols, the conductors, the bulb, and the switch. Figure 4-6 shows the symbols that you’ll need to produce a complete schematic of this flashlight. Again, you should draw the symbols in the same sequence as the components appear in the pictorial. Figure 4-7 shows the result. The two cell symbols are drawn separately, connected in series, with polarity markings for each one. In the series connection, the positive terminal of one cell goes to the negative terminal of the other. You’ll use two conductors from the cell terminals and a third conductor to connect the switch to the light bulb, and you might also need a fourth conductor connecting the cells together to form a battery (unless the cells rest directly against each other, a common arrangement in manufactured flashlights). Figure 4-7 shows the switch in the “off” position.
图 4-5 手电筒电路示意图，该电路使用两个串联的电化学电池、一些导线、一个开关和一个白炽灯泡。
FIG. 4-5 Pictorial of a flashlight circuit using two electrochemical cells in series, some wire, a switch, and an incandescent bulb.
图 4-6 双节电池开关手电筒的组件符号：电池 (A)、导线 (B)、灯泡 (C) 和开关 (D)。
FIG. 4-6 Symbols for components in the two-cell switched flashlight: Cell (A), wire (B), bulb (C), and switch (D).
图 4-7 双节电池开关手电筒示意图。
FIG. 4-7 Schematic of the two-cell switched flashlight.
图 4-8是射频场强计的示意图。无线电工程师有时会使用这种类型的仪表来检测特定位置是否存在射频电磁场。如果您想定位对业余无线电或短波无线电接收机造成射频干扰的源头，您会发现这个设备非常实用。该电路包含一个小型鞭状天线、一个射频二极管、一个微安表（一种以百万分之一安培为单位的灵敏电流表）和一个电感器。
Figure 4-8 is a pictorial drawing of an RF field-strength meter. Radio engineers sometimes use this type of meter to 2see whether or not an RF electromagnetic (EM) field exists at a given location. You’ll find this device handy if you want to locate the source of something that’s causing RF interference to your amateur or shortwave radio receiver. The circuit consists of a small whip antenna, an RF diode, a microammeter (a sensitive current meter graduated in millionths of an ampere), and an inductor.
图 4-8 射频场强计电路示意图。
FIG. 4-8 Pictorial of an RF field-strength meter circuit.
要绘制此电路的原理图，您必须了解天线、电感器（本例中为空芯线圈）、微安表和二极管的符号。图 4-9分别显示了这些符号。您应该按照图示顺序连接这些符号。
To draw a schematic of this circuit, you must know the symbols for an antenna, an inductor (in this case an air-core coil), a microammeter, and a diode. Figure 4-9 shows these symbols individually. You should connect the symbols in the same sequence as you do when you follow the pictorial around.
图 4-10是图 4-8所示场强计的示意图。该图仅用示意图符号替换了图示符号。组装场强计时，各部件的物理位置不必与示意图所示完全相同，但应按照示意图所示的顺序连接。
Figure 4-10 is a schematic of the field-strength meter shown pictorially in Fig. 4-8. This drawing involves nothing more than substitution of the schematic symbols for the pictorial symbols. When you assemble the meter, the parts need not go in the same physical locations as the schematic implies, but you should connect them in the same sequence as the schematic indicates.
图 4-9 场强计中各组件的符号：天线 (A)、线圈 (B)、微安表 (C) 和二极管 (D)。
FIG. 4-9 Symbols for the components in the field-strength meter: Antenna (A), coil (B), microammeter (C), and diode (D).
图 4-10 射频场强计示意图。
FIG. 4-10 Schematic of the RF field-strength meter.
现在我们来看一个更复杂的电路。图 4-11是一个电源的原理图，它将市电交流电转换为类似电池的直流电。从左到右阅读电路图，你会看到电源插头通过保险丝连接到变压器初级绕组（两条垂直线左侧的线圈）。变压器次级绕组（两条垂直线右侧的线圈）的顶端连接到整流二极管的阳极。二极管的阴极连接到电解电容器的正极。电容器的负极（图中未标注，因为你可以……）（仅凭“+”号即可推断）连接到变压器次级的下端。一个固定电阻与电容器并联。直流输出出现在最右侧，即电阻两端。
Now let’s examine a more complicated circuit. Figure 4-11 is a schematic of a power supply that produces battery-like DC from utility AC. As you read the diagram from left to right, you’ll see that the power plug goes to the transformer primary winding (the coil on the left-hand side of the two vertical lines) through a fuse. The top end of the transformer secondary winding (the coil on the right-hand side of the two vertical lines) connects to the anode of a rectifier diode. The diode’s cathode goes to the “plus” side of an electrolytic capacitor. The “minus” side of the capacitor (not labeled because you can infer it on the basis of the “plus” sign alone) goes to the bottom end of the transformer secondary. A fixed resistor shunts (connects in parallel with) the capacitor. The DC output appears at the extreme right, across the resistor.
图 4-11 简单直流电源的示意图。
FIG. 4-11 Schematic of a simple DC power supply.
您可以根据图 4-11搭建一个实际的电源，其物理尺寸和重量取决于您所需的电压和电流。由于任何直流电源都具有极性输出，因此您应该使用“正”和“负”符号来表示哪个输出端提供正电压，哪个输出端提供负电压。任何使用单个二极管、电容器和电阻器的电源都将采用这种配置。无论直流输出端提供 5V/1A 还是 5000V/50A，原理图看起来都一样。但是，图 4-11并未说明变压器、二极管、电容器和电阻器能够承受多少伏特或安培的电流。
The physical size and weight of a real-world power supply, which you can build on the basis of Fig. 4-11, will depend on the voltage and current that you want to get from it. Because any DC power supply has a polarized output, you should use “plus” and “minus” signs to show which output terminal provides the positive voltage and which terminal provides the negative voltage. Any power supply that uses a single diode, capacitor, and resistor will have this configuration. Whether the DC output terminals provide 5 V at 1 A or 5000 V at 50 A, the schematic will look the same. But Figure 4-11 says nothing about how many volts or amperes the transformer, diode, capacitor, and resistor can handle.
组件标签
Component Labeling
图 4-12是与图 4-11所示电路相同的电路原理图，但图中每个元件都标有字母/数字组合。这些标识均对应图底部的列表。现在您知道，该电源使用一个变压器，其初级绕组额定电压为 120 VAC，次级绕组输出电压为 18 VAC。电路中包含一个额定峰值反向电压(PIV) 为 50 伏、峰值正向电流为 1 安的二极管；一个 100微法、50 伏的电容器；以及一个 10,000 欧姆、1 瓦的碳膜电阻。保险丝的额定最大电流为 0.5 安/120 伏。
Figure 4-12 is a schematic of the same circuit as the one shown in Fig. 4-11, but in this case each component has an alphabetic/numeric designation. These designators all refer to a list at the bottom. Now you know that this power supply uses a transformer with a primary winding rated at 120 VAC and a secondary winding that yields 18 VAC. The circuit has a diode rated at 50 peak inverse volts (PIV) and a peak forward current of 1 A; a 100 microfarad, 50 V capacitor; and a 10,000 ohm, 1 W carbon resistor. The fuse is rated for a maximum current of 0.5 A at 120 V.
图 4-12 电源原理图，包括元件编号和规格。
FIG. 4-12 Schematic of the power supply, including component designators and specifications.
行业内各元件的标识字母相当标准。在图 4-12中，每个字母后都跟着数字 1。例如，标识 T1 表示该元件是变压器 (T)，并且它是图中第一个出现的变压器元件。如果该电路有两个变压器，则其中一个标记为 T1，另一个标记为 T2。这些数字表示元件在元件列表中的位置或顺序。二极管的参考编号为 D1，其中 D 是大多数二极管的标准缩写。然而，标准化并非普遍适用！在某些情况下，二极管可能标记为 SR1，其中 SR 代表硅整流器。一些齐纳二极管的标签为 ZD1、ZD2 等。只要将元件标识符写在相应符号旁边，标签本身并不重要。即使将 D1 替换为 SR1，只要缩写靠近二极管符号，读者仍然能够知道该缩写与二极管符号对应。
The letters that identify each component are fairly standard in the industry. In Fig. 4-12, a numeral 1 follows each letter. The designation T1, for instance, indicates that the component is a transformer (T) and that it’s the first such component referenced. If this circuit had two transformers, then one of them would bear the label T1 and the other one would bear the label T2. The numerals reference the position or order on the components list. The diode has the reference D1, with D serving as the standard abbreviation for most diodes. Standardization is not universal, however! In some instances, the diode might bear the label SR1, where the letters SR stand for silicon rectifier. Some Zener diodes have labels such as ZD1, ZD2, and so on. The labels don’t matter as long as you write the component designators right next to the corresponding symbols. If you replaced the designation D1 with SR1, your readers would still know that the abbreviation went with the symbol for the diode, as long as you put the abbreviation close to the symbol.
在图 4-12所示的电路中，您可能不想在每个元件名称旁边都加上数字，因为搭建电路只需要每种元件一个！您可以用 P 表示插头，F 表示保险丝，T 表示变压器，D 表示二极管，C 表示电容器，R 表示电阻器。或者，如果您确信读者都熟悉这些符号，您可以完全省略这些标识。然而，标准的电路图绘制规范要求您始终包含字母和数字，即使某种类型的元件只有一个。
In the situation of Fig. 4-12, you might not want to include a numeral next to each component designation, because you need only one of each component to build the circuit! You could write P for the plug, F for the fuse, T for the transformer, D for the diode, C for the capacitor, and R for the resistor. Or, if you had confidence that your readers knew all the symbols, you could leave out the designators altogether. Nevertheless, standard diagramming practice requires that you always include a letter and a numeral, even if only one of a certain component type exists.
在一个复杂的电子系统中，你可能会发现数百个相同类型的元件（例如电阻器），其中许多属于同一系列。例如，如果你看到元件编号为 R101，那么你就知道该系统至少包含 101 个电阻器。如果你想知道电阻器 R101 的类型和阻值，你需要查找元件列表中的 R101 以获取其规格参数。
In a complicated electronic system, you might find several hundred components of the same type (resistors, for example), many of which come from the same family. For instance, if you see the designation R101, then you know that the system contains at least 101 resistors. If you want to know the type and value of resistor R101, you will have to look up R101 in the components list to find its specifications.
表 4-1列出了电路图中大多数电子元件的标准字母表示法。在实际文档中，由于绘图者或电路设计者的个人习惯，这些缩写可能会有所不同。大多数表示法由元件名称的首字母组成。如果元件名称比较复杂，例如“硅控整流器”，则可以使用每个单词的首字母，例如 SCR1。电阻器用 R 表示，电容器用 C 表示，保险丝用 F 表示，以此类推。当然，也会出现冲突。例如，如果要表示继电器，则必须使用 R 以外的字母，因为 R 表示电阻器。同样，如果要表示晶体，则不能使用 C，因为 C 表示电容器。如果您在阅读和绘制电路图时经常参考表 4-1，一段时间后就能掌握其中的所有信息。
Table 4-1 shows the standard letter designations for most types of electronic components that you’ll see in schematic diagrams. Some of these abbreviations vary in real-world documentation, depending upon the idiosyncrasies of the person making the drawing or designing the circuit. Most designations comprise the first letter or letters of the component names. If the component has a complex name, such as silicon-controlled rectifier, the first letters from each word can be used, so you get SCR1. You’ll designate a resistor by R, a capacitor by C, a fuse by F, and so on. Conflicts arise, of course. If you want to specify a relay, you must use some letter other than R, because R indicates a resistor. The same thing happens if you want to label a crystal; you can’t use C because that letter refers to a capacitor. If you examine Table 4-1 often as you read and draw schematic diagrams, you’ll absorb all its information after awhile.
表 4-1 原理图中常见的元件符号的字母缩写。
TABLE 4-1 Letter abbreviations for component symbols that you’ll often see in schematic diagrams.
图 4-13的电源采用全波桥式整流器，并配备了比图 4-12电路中单个电容更好的纹波滤波器。电感 L1 是一个滤波扼流圈，它与电容 C1 配合，能够很好地平滑直流电压，使其与电池的输出非常接近。稳压二极管 D5 可防止直流输出电压过高。12伏。限流电阻器可以防止D5烧毁，但同时也限制了电源与任何需要大电流的电器一起使用。（如果向电源输入的电流过大，输出电压将降至12伏以下。）
The power supply of Fig. 4-13 has a full-wave bridge rectifier along with a better ripple filter than the lone capacitor in the circuit of Fig. 4-12. The inductor, L1, is a filter choke, which, along with capacitor C1, does an excellent job of smoothing out the DC so it closely mimics what you’d get from a battery. The Zener diode, D5, keeps the DC output voltage from exceeding 12 V. The current-limiting resistor keeps D5 from burning out, but it also prevents you from using the power supply with any appliance that demands a lot of current. (If you ask the supply for too much current, the output voltage will drop below 12 VDC.)
图 4-13 采用全波桥式整流（四个整流二极管）和齐纳二极管稳压的电源原理图。
FIG. 4-13 Schematic of a power supply that uses full-wave bridge rectification (four rectifier diodes) and Zener-diode voltage regulation.
图 4-14展示了一个倍压电源电路。两个电容 C1 和 C2 在经过二极管 D1 和 D2 后，从变压器次级输出端充电。由于这两个电容串联，它们就像串联电池一样，可以提供两倍的电压。但是，这里有个问题！倍压电源只有在低电流下才能正常工作。如果从这类电源中汲取过大的电流，就会“消耗”电容的电量，导致电压下降。此外，由于 C1 和 C2 无法很好地平滑直流电压，还会产生更大的纹波。
Figure 4-14 shows the circuit for a voltage-doubler power supply. The two capacitors, C1 and C2, charge up from the full transformer secondary output after going through diodes D1 and D2. Because the two capacitors are connected in series, they behave like batteries in series, giving you twice the voltage. But there’s a catch! A voltage-doubler power supply works well only at low current levels. If you demand too much current from one of these supplies, you’ll “draw down” the capacitors and the voltage will drop. You’ll end up with more ripple too, because C1 and C2 won’t be able to smooth out the DC very well.
图 4-14 倍压电源的示意图。
FIG. 4-14 Schematic of a voltage-doubler power supply.
在图 4-13和4-14中，每种元件的字母标记相同，但数字依次递增，直至达到元件总数。例如，在图 4-13中，您可以看到二极管 D1 到 D5，因为电路中包含五个二极管。（R1 右侧的齐纳二极管的字母标记与整流二极管相同，但您可以通过符号中的弯曲线来识别它是齐纳二极管。）所有其他元件每种类型都只有一个。在图 4-14中，您可以看到两个二极管、两个电容器和两个电阻器，因此 D、C 和 R 的数字递增至 2。电路中只有一个变压器，因此您只会看到字母 T 后面的数字 1。
In Figs. 4-13 and 4-14, the letter designations are the same for each component type, but the numerals advance, one by one, up to the total number of units. So, for example, in Fig. 4-13 you see diodes D1 through D5 because the circuit contains five diodes. (The Zener diode to the right of R1 has the letter D just like the rectifier diodes have, but you can tell it’s a Zener diode because of the bent line in the symbol.) All the other components have only one of each type. In Fig. 4-14, you see two diodes, two capacitors, and two resistors, so the numerals for D, C, and R go up to 2. The circuit has only one transformer, so you’ll see only the numeral 1 after the letter T.
原理图不像照片或详细图示那样能展现设备的全部物理细节。原理图只展示电路的运行方式，仅此而已！原理图能帮助你在组装电路时建立正确的电气连接。它还能帮助你在测试、调整、调试或排除电路故障时定位各个元件。
Schematics don’t reveal every physical aspect of a device the way photographs or detailed pictorials can do. Schematics show you schemes, that’s all! A schematic allows you to make the correct electrical connections as you assemble a circuit. It also lets you locate individual components when you test, adjust, debug, or troubleshoot the circuit.
如果您觉得前面的讨论过于哲学化，或许一个实际的例子能帮助您理解。在电路图中，实线代表导体。这条导体可能是导线，也可能不是！它可能是元件引脚，也可能是印刷电路板 (PC)上的金属箔。连接两个元件是否需要导线，取决于这两个元件在实际电路布局中的距离。请看图 4-15的简单电路图。该电路包含三个电阻，它们并联连接。如果您严格按照电路图进行描述，可以得出以下结论。
If you find the foregoing discussion too philosophical, maybe a real-world example will clear things up. In a schematic, a solid line represents a conductor. Maybe that conductor is a wire, but maybe not! It might be a component lead or a foil run on a printed circuit (PC) board. Whether or not you need a length of wire to connect two components will depend on how close together those components reside in the physical layout. Examine the simple schematic of Fig. 4-15. The circuit contains three resistors, all of which go together in a parallel arrangement. If you take the schematic literally and describe the situation with rigor, you can recite the following facts.
• 一根导线将 R1 的左侧连接到 R2 的左侧。
• One conductor connects the left-hand side of R1 to the left-hand side of R2.
• 第二根导线将 R2 的左侧连接到 R3 的左侧。
• A second conductor connects the left-hand side of R2 to the left-hand side of R3.
• 第三根导线将 R1 的右侧连接到 R2 的右侧。
• A third conductor connects the right-hand side of R1 to the right-hand side of R2.
• 第四根导线将 R2 的右侧与 R3 的右侧连接起来。
• A fourth conductor connects the right-hand side of R2 to the right-hand side of R3.
• 第五根导线连接到所有三个电阻器的左侧，并向左延伸，从视线中消失。
• A fifth conductor connects to the left-hand sides of all three resistors and runs off to the left, out of sight.
• 第六根导线连接到所有三个电阻器的右侧，并向右延伸，看不见。
• A sixth conductor connects to the right-hand sides of all three resistors and runs off to the right, out of sight.
实际上，你可以通过将导线连接到电阻器的引脚来实现部分或全部连接，但如果实际应用中元件之间的距离足够近，则可以直接使用引脚进行连接。此时，图 4-15将表示图 4-16中所示的物理结构。
In practice, you can make some or all of these connections by attaching wires to the resistor leads, but if the components lie close enough to each other in the real world, you can use the leads themselves to make the connections. Then Fig. 4-15 will represent the physical arrangement shown pictorially in Fig. 4-16.
如果你想遵循良好的工程原理，就应该尽可能地简化电子电路（使其更加紧凑可靠），尽量减少点对点连接，并尽可能利用元件引脚进行互连。当然，在上面的例子中，如果三个电阻必须位于电路的不同位置，且彼此距离较远，那么就需要使用单独的互连导线连接它们。
If you want to follow good engineering principles, you’ll make all of your electronic circuits as compact (and dependable) as possible by using a minimum of point-to-point wiring and trying to make the component leads serve for interconnection purposes whenever you can. Of course, in the above example, if the three resistors had to go in different parts of the circuit separated by long distances, then you’d have to use separate interconnecting conductors between them.
图 4-15 三个电阻并联的示意图。
FIG. 4-15 Schematic of three resistors connected in parallel.
图 4-16 三个电阻器并联，引脚绞合在一起的示意图。
FIG. 4-16 Pictorial of three resistors connected in parallel with their leads twisted together.
利用原理图进行故障排除
Troubleshooting with Schematics
工程师和技术人员使用电路图来设计电子系统，电路图在设备出现故障时也至关重要。然而，仅仅会读电路图是不够的。你还必须了解各个组件的功能，以及不同的电路如何在整个系统中协同工作。无论你的电子故障排除能力多么强，如果没有完整、准确、清晰的硬件电路图，看似简单的维修工作也可能变成棘手的难题。
Engineers and technicians use schematics to design electronic systems, and schematics can also prove valuable for troubleshooting equipment when problems develop. Nevertheless, merely knowing how to read schematics isn’t enough. You must also know what the individual components do, and how diverse circuits can work together in the complete system. No matter how proficient you get at electronics troubleshooting, seemingly simple repair jobs can morph into huge headaches without complete, accurate, and clear schematic representations of the hardware.
当你根据电路图搭建电路时，实际的电路很少与电路图在物理上完全一致。你不可能仅仅按照电路图上的位置来搭建复杂的电子系统。电路图只是为了方便阅读而将符号排列在纸上。电路图是二维的，而现实世界中的元件、电路、设备和系统都是三维的。你只需要看看像电视机或电脑这样的大型电子系统的内部结构，就能意识到如果没有电路图的帮助，在排除此类系统的故障时会面临多么复杂的问题。
When you build a circuit on the basis of a schematic, the physical object rarely bears much physical resemblance to the diagram. You can’t build a complex electronic system by placing the components in the same geometric positions as they appear in the schematic. The schematic arranges the symbols on the page for easy reading. Schematics occupy two dimensions, whereas real-world components, circuits, devices, and systems occupy three dimensions. You need only to look inside of a major electronic system such as a television set or computer to realize the complexities that you’d face in troubleshooting such a system without the help of a schematic.
如果您对电子元件及其在各种电路中的工作原理有一定的了解，那么您可以利用电路图大致判断出问题可能出现的位置。然后，通过测试这些关键点的各种电路参数，并将测试结果与电路图上这些点的预期值进行比较，您可以快速评估故障所在。例如，如果电路图显示电路中两个元件之间直接连接，但用欧姆表测量发现两者之间存在高电阻，那么您可以推断是导线断裂或触点松动。如果电路图显示两个元件之间只有一个电容器（没有其他电路绕过它），而用欧姆表测量发现电阻为零欧姆或只有几欧姆，那么您可以推断是电容器短路，需要更换。
If you know a fair amount about electronic components and how they operate in various circuits, then you can use a schematic to get a good idea of where a particular problem might occur. Then, by testing various circuit parameters at these critical points and comparing your findings with what the schematic diagram says should exist at those points, you can make a quick assessment of the trouble. For example, if a schematic shows a direct connection between two components in a circuit but a check with an ohmmeter reveals high resistance between the two, then you can assume that a conductor has broken or a contact has shaken loose. If a schematic shows only a capacitor between two components (with no other circuit routes around it) and a reading with your ohmmeter shows zero ohms or only a couple of ohms, then you can assume that the capacitor has shorted out and you’ll have to replace it.
电子故障排除和电路图阅读的初学者有时会误以为专业人士只需查看电路图就能立即将问题定位到元件层面。这种理想化的情况或许适用于一些简单的电路，但在复杂的电路设计中，情况就复杂得多。电路图可以帮助技术人员对问题所在或原因做出合理的推测，但全面的诊断几乎总是需要进行测试。
Beginners to electronics troubleshooting and diagram reading sometimes assume that a professional can instantly isolate a problem to the component level by looking at the schematic. This idealized state of affairs might prevail for a few simple circuits, but in complex designs the situation grows more involved. A schematic can help a technician make educated guesses as to where a problem lies or what causes it, but an exhaustive diagnosis nearly always requires testing.
假设某个电路无法启动，并且当你检查电路图中所示的所有测试点时，都检测不到任何电压。很可能根本没有电流流过该电路。然而，你无法从这一观察结果中确切地知道故障原因。请问自己以下几个问题。
Suppose that a circuit won’t activate, and you can’t detect any voltage when you check all the test points shown in its schematic. In all probability, no current is passing through the circuit at all. However, you don’t know from this observation exactly what has caused the failure. Ask yourself the following questions.
• 电源中的某个元件是否损坏了？
• Has one of the components in the power supply gone bad?
• 你是不是不小心把电源线从墙上的插座拔出来了？
• Have you accidentally pulled the power cord from the wall outlet?
• 电源输出端和设备输入端之间是否有导线断裂？
• Has a conductor broken between the power-supply output and the device input?
• 电源保险丝烧断了吗？
• Has the power-supply fuse blown?
在这种情况下，您需要参考电路图，并按照所有标准测试步骤进行操作。您可能会找到电路图上标明的电源输入测试点。如果您检查该点的电压，并且电压正常，则可以推断问题出在电路的更远处。通过电路图和测试仪器的读数，您可以从电路中运行正常的点开始，逐步向前排查，直到找到电路出现异常的位置，从而有条不紊地查找并隔离问题。
In a situation like this, you’ll want to consult the schematic as you go through all of the standard test procedures. You might find the test point that serves as the power supply input, indicated on the schematic. If you check the voltage at this point and it appears normal, then you can assume that the problem lies somewhere further along in the circuit. The schematic and the test instrument readings allow you to methodically search out and isolate the problem by starting at a point in the circuit where operation appears normal and proceeding forward until you get to the point where the circuit behaves abnormally.
你也可以反向测试。如果电源没有输出，那就说明你必须反向查找故障点。你需要不断测试，直到找到正常工作点，然后检查该点附近的所有元件。借助电路图，你可以跟踪测试进度，并将故障区域缩小到两个点之间的某个位置（故障点位于距离输出端最远的位置，而正常点位于距离输入端最远的位置）。这种缩小范围的方法很可能最终将故障定位到单个元件或电路连接上。
You can test in the other direction as well. If no output comes from the power supply, you know that you must search backward toward the trouble point. You’ll keep testing until you reach a point of normal operation and then check all the components in that vicinity. With the help of a schematic, you’ll follow your progress and narrow the problem area down to something between two points (the point farthest back from the output at which the problem exists, and the point furthest forward from the input where things test normal). Chances are good that this narrowing process will isolate the trouble to a single component or circuit connection.
请返回并再次查看图 4-7中的手电筒电路。虽然原理图上没有标明，但两个串联的电池应该产生 3V 直流电压，因为一个典型的手电筒电池本身就能提供 1.5V 直流电压，而直流电压在串联电路中会叠加。有些电路图会提供电压测试点以及你应该看到的最大值/最小值，但这个简单的示例没有。
Go back and look again at the flashlight circuit of Fig. 4-7. Although the schematic doesn’t say so, the two batteries in series should yield 3 VDC, because a typical flashlight cell provides 1.5 VDC all by itself, and DC voltages add up in series connections. Some schematics provide voltage test points and maximum/minimum readings that you should expect, but this simple example doesn’t.
假设手电筒停止工作，您决定使用万用表（也称电压-欧姆-毫安表）测试电路，如图 4-7所示。首先，您可以测量各节电池的电压。将万用表的正极探针连接到电池的正极，负极探针连接到负极，您应该在每个电池两端都读到 1.5V 的电压。如果两个电池的读数均为 0V，则说明两个电池都已耗尽电量。如果一个电池读数正常，另一个电池读数为 0V，那么理论上您只需更换看起来“损坏”的电池即可。（实际上，如果一组电池中有一个或多个电池看起来“损坏”或“即将损坏”，即使其中一些电池测试正常，也应该同时更换整组电池。）如果两个电池都显示正常，则可以测试灯泡两端的电压。在正常工作状态下，开关关闭时，灯泡两端的电压应为 3V。如果你确实在这里观察到了 3V 的电压，那么你可以通过查看电路图来诊断问题。灯泡肯定烧坏了！电路图显示，如果灯泡能导通，电流就应该流过它，所以它应该会亮。但如果灯丝断了，电流就无法流过灯泡，因此它不会亮。事实上，灯泡烧坏后，电路中任何地方都不会有电流通过。
Suppose that the flashlight has stopped working, and you decide to test the circuit with a volt-ohm-milliammeter (VOM), also called a multimeter, with the help of Fig. 4-7. First of all, you can measure the individual voltages across the cells. With the meter’s positive probe placed at the positive cell terminal and the negative probe at the negative terminal, you should get a reading of 1.5 V across each cell. If both cells read 0 V, then you know that both cells have lost all their electrical charge. If one cell reads normal and the other one reads 0 V, then in theory you should only have to replace the cell that appears “dead.” (In practice, if one or more cells in a set appears “dead” or “dying,” you should replace the whole set at the same time, even if some of them test okay). If both cells appear normal, then you can test the voltage across the bulb. Here, you should expect a reading of 3 V under normal operation with the switch closed. If you do indeed observe 3 V here, then you can diagnose the problem by looking at the schematic. The bulb must have burned out! The schematic shows you that current should pass through the bulb if it can conduct, so it must light up. But if the filament has broken, no current can flow through the bulb, so it won’t light up. In fact, with a burned-out bulb, no current will flow anywhere in the circuit.
另一方面，假设你测得两节电池两端电压为 3V，但灯泡两端电压为 0V。显然，灯泡和两节电池之间的电路某处断路了。这里涉及三根导线：一根连接电池负极和灯泡一端，一根连接电池正极和开关，还有一根连接开关和灯泡另一端。你可以得出结论，其中一根导线断路了。可能是导线断裂、导线与电池连接处接触不良，或者开关本身有故障。您可以一边查看电路图，一边测试开关是否损坏：将万用表负极探针接电池负极，正极探针接开关输入端。如果电压读数正常，则说明开关有故障。如果仍然没有电压读数，则说明某根导线松动或断裂。
On the other hand, let’s say that you see 3 V across the pair of cells, but 0 V at the light bulb. Apparently, a break exists somewhere in the circuit between the bulb and the two-cell battery. Three conductors are involved here: one between the negative terminal of the battery and one side of the bulb, another between the positive battery terminal and the switch, and another between the switch and the other side of the bulb. You can conclude that one of the conductors has broken, a contact has been lost where the conductor attaches to the battery, or the switch is defective. While you keep an eye on the schematic, you can test for a defective switch by placing the negative meter probe on the negative battery terminal and the positive probe on the input to the switch. If you see a normal voltage reading, then the switch must be defective. If you still get no voltage reading, then one of the conductors must have come loose or broken.
诚然，刚才描述的情况只是使用电路图进行故障排除的一个基本示例。但假设手电筒是按照你完全不了解的全新设计制造的，那么除了使用万用表进行标准测试外，你还需要电路图作为辅助工具。每当你测试类似复杂的电子电路时，都会用到同样的方法。
Admittedly, the scenario just described presents only a basic example of troubleshooting using a schematic. But imagine that the flashlight has been built according to some new design that you know nothing about. Then you’ll need the schematic an adjunct to the standard test procedures with the VOM. You’ll use this same procedure whenever you test complex electronic circuits of a similar nature.
更复杂的图表
A More Sophisticated Diagram
图 4-17显示了一个便于故障排除技术人员使用的电路原理图。该电路包含一个 NPN 双极型晶体管以及一些电阻和电容。请注意，测试点（缩写为 TP）位于三个不同的位置：TP1 位于晶体管的发射极，TP2 位于基极，TP3 位于集电极。
Figure 4-17 shows a schematic presented in a form that can assist a troubleshooting technician. The circuit has a single NPN bipolar transistor along with some resistors and capacitors. Note that test points (abbreviated TP) exist at three different locations: TP1 at the emitter of the transistor, TP2 at the base, and TP3 at the collector.
如果您需要对这个电路（它恰好是一个低功率放大器，类似于老式收音机或超声波开关中的那种）进行故障排除，请将万用表依次连接到机箱地线和每个测试点之间。记录万用表读数，并将其与已知的正常值进行比较。
If you need to troubleshoot this circuit (which happens to be a low-power amplifier of the sort you might find in a vintage radio receiver or ultrasound-actuated switch), you’ll connect your VOM between chassis ground and each test point in turn. You’ll note the meter readings and compare them with known normal values.
在许多电路中，实际电压值可能与设计值偏差高达 20%；如果此信息对您很重要，通常可以在电路图底部或相关文档中找到它。如果读数落在已知的误差范围内（称为元件容差），则可以合理地认为电路的这一部分工作正常。但是，如果读数远远超出容差范围，则应怀疑相关电路部分或为其供电的其他电路存在问题。
In many circuits, the actual voltages can deviate from the design values by up to 20 percent; if this information is important, you’ll usually find it at the bottom of the schematic or in the accompanying literature. If you get readings that fall within this known error range (called the component tolerance), then you can reasonably assume that this part of the circuit is working properly. However, if you get readings far outside of the tolerance range, then you should suspect a problem with the associated circuit portion, or possibly with other circuits that feed it.
许多电子设备的电路图，尤其是那些使用包含各个组件的套件组装的“项目”的电路图，不仅能帮助您进行故障排除，还能指导您在组装完成后、投入使用前必须进行的测试和校准程序。此外，说明书可能还会包含图示，向您展示每个元件在电路板或机箱上的位置。这样，您不仅可以根据电路的电气细节来理解电路，还可以根据实际的物理路径来理解电路。
Many schematics that accompany electronic equipment, especially “projects” that you build from kits containing individual components, include information that can help you not only in troubleshooting, but also in the testing and alignment procedures that you must follow after you’ve completed the assembly process but before you put the equipment into service. As a further aid, the literature might include pictorials that show you where each part belongs on the circuit board or chassis. That way, you can follow the circuit not only according to its electrical details, but also along the physical pathways as they look in real life.
根据标准电路原理图绘制规范，每个元件都应带有唯一的字母/数字标签来标识，如图4-17所示。然而，一些其他的标签形式也是可以接受的。图 4-18显示与图 4-17相同的电路，但该图没有字母/数字标识或测试点。这些元件仅通过电路图符号及其电气参数或行业标准元件代号来识别。在所示示例中，您知道晶体管是 2N2222 型，电阻器的阻值分别为 470 欧姆、33kΩ（33,000 欧姆）、330kΩ（330,000 欧姆）和 680 欧姆。输入电容的值为 0.01 微法 (µF)，输出电容的值为 0.1 µF。并联在 470 欧姆电阻两端的发射极电容的值为 4.7 µF。
According to standard schematic drawing practice, every component should bear a unique alphabetic/numeric label to designate it, as you see in Fig. 4-17. However, a few alternative labeling forms are also acceptable. Figure 4-18 shows the same circuit as the one in Fig. 4-17, but the diagram contains no alphabetic/numeric designations or test points. The components are identified only by their schematic symbols along with their electrical values or industry standard part designations. In the example shown, you know that the transistor is a 2N2222 type, and that the resistors have values of 470, 33k (33,000), 330k (330,000), and 680 ohms. The input capacitor has a value of 0.01 microfarad (µF), and the output capacitor has a value of 0.1 µF. The emitter capacitor, which goes across the 470-ohm resistor, has a value of 4.7 µF.
图 4-17 放大器电路示意图，包括元件标识符和三个测试点 (TP) 位置。
FIG. 4-17 Schematic of an amplifier circuit that includes component designators and three test point (TP) locations.
图 4-18为 图 4-17所示放大器电路的原理图，但图中显示的是元件值而非顺序编号。所有电容单位均为微法 (µF)。所有电阻单位均为欧姆 (Ω)；k = 1000。
FIG. 4-18 Schematic of the amplifier circuit of Fig. 4-17, but with component values rather than sequential designators. All capacitances are in microfarads (µF). All resistances are in ohms (V); k = 1000.
原理图/框图混合
Schematic/Block Hybrids
有时你会遇到一种混合图，它将方框和原理图符号结合在一起。图 4-19就是一个例子，当你想要展示系统中特定电路的细节并阐明该电路与其他系统部分的关系时，这种方法非常有效。图 4-19的原理图部分展示了一个缓冲器，这种缓冲器有时会出现在无线电发射机中。带标签的方框分别表示振荡器（位于缓冲器之前）和放大器（位于缓冲器之后）。
Once in awhile you’ll encounter a hybrid drawing that has blocks and schematic symbols combined. Figure 4-19 provides an example of this approach, which works well when you want to show the details of a particular circuit within a system and clarify that circuit’s relationship to other parts of the system. The schematic portion of Fig. 4-19 shows a buffer of the sort that you’ll sometimes find in a radio transmitter. The labeled blocks portray an oscillator (which precedes the buffer) and an amplifier (which follows the buffer).
图 4-19 振荡器、缓冲器和放大器系统的混合框图/原理图，显示了缓冲器电路的原理细节。
FIG. 4-19 Hybrid block/schematic diagram of an oscillator, buffer, and amplifier system, showing the schematic details of the buffer circuit.
此图有两个用途。首先，在阅读原理图部分时，您可以研究缓冲电路的元件构成。其次，您可以清楚地了解缓冲器在整个系统中相对于其他电路的位置。图 4-19显示缓冲器的输入来自晶体振荡器，其输出发送到放大器。另一种原理图/框图组合可能描述了同一系统的不同部分。
This diagram serves two purposes. First, as you read the schematic portion, you can study the component makeup of the buffer circuit. Second, you get a good idea as to the buffer’s place in the overall system relative to the other circuits. Figure 4-19 tells you that the buffer receives its input from a crystal-controlled oscillator, and also that the buffer sends its output to an amplifier. Another schematic/block diagram combination might describe a different part of this same system.
图 4-20是与图 4-19所示系统相同的混合图。在这个版本中，您可以详细地看到振荡器电路的原理图，而缓冲器和放大器电路则被简化为模块。图 4-20与图 4-19一样，都表明振荡器的输出连接到缓冲器，然后信号传递到放大器。将图 4-19和图4-20放在一起观察，您可以大致了解信号进入放大器之前的所有系统细节。图 4-20的振荡器部分揭示了该电路能够产生莫尔斯电码信号，因为它包含一个电报键，这是一个特殊的开关 (S1)。
Figure 4-20 is a hybrid diagram of the same system that Fig. 4-19 shows. In this version, you see the oscillator circuit in schematic detail, but the buffer and amplifier circuits are condensed into blocks. Figure 4-20 tells you, as Fig. 4-19 did, that the oscillator output goes to the buffer, and the signal then passes to the amplifier. As you look at Figs. 4-19 and 4-20 together, you can mentally envision all the system details up to the point where the signal enters the amplifier. The oscillator portion of Fig. 4-20 reveals the fact that the circuit can generate Morse code signals because it contains a telegraph key, which is a specialized switch (S1).
现在让我们回顾一下您在图 2-1中看到的电源框图。图 4-21包含该系统的示意图（A 点）以及图 2-1的副本（B 点）。图 A 展示了电源中的所有组件，而图 B 仅显示了各个电路级。图 4-22突出显示了图 4-21A的示意图，以展示图 4-21B中各个模块的内容，但省略了字母数字组件标识符，以尽量减少混乱。
Now let’s recall the block diagram of the power supply that you saw back in Fig. 2-1. Figure 4-21 comprises a schematic representation of that system (at A) along with a duplicate of Fig. 2-1 (at B). Drawing A portrays all the individual components in the power supply, while drawing B shows only the stages. Figure 4-22 highlights the schematic of Fig. 4-21A to reveal the contents of the blocks in Fig. 4-21B, but leaves out the alphabetic-numeric component designators to minimize clutter.
图 4-20 图 4-19系统的混合框图/原理图，显示了振荡器电路的原理细节。
FIG. 4-20 Hybrid block/schematic diagram of the system of Fig. 4-19, showing the schematic details of the oscillator circuit.
图 4-21电源原理图（A 处），例如您在 图 2-1中看到的框图（此处在 B 处重现）。
FIG. 4-21 Schematic of a power supply (at A) such as the one in the block diagram you saw back in Fig. 2-1 (reproduced here at B).
图 4-22 图 4-21A与图 4-21B的关系如下。为了避免画面杂乱，省略了元件标识符。
FIG. 4-22 Here’s how Fig. 4-21A relates to Fig. 4-21B. Component designators have been omitted to avoid clutter.
真空管射频放大器
A Vacuum-Tube RF Amplifier
图 4-21和4-22所示的电源将为图 4-19和4-20所示的无线电报发射机的振荡器和缓冲器部分供电。但是，12V 直流电压不足以驱动构成最终电路的放大器。这是发射机的一部分，因为那个放大器使用了真空管！如今，除了那些旨在提供高功率输出（数百甚至数千瓦）的放大器之外，你很少能看到真空管了。但“很少”并不意味着“从不”。
The power supply diagrammed in Figs. 4-21 and 4-22 will operate the oscillator and buffer parts of the radiotelegraph transmitter of Figs. 4-19 and 4-20. But 12 VDC will not suffice for the amplifier that constitutes the final part of the transmitter, because that amplifier employs a vacuum tube! You’ll rarely see tubes nowadays except in amplifiers designed to provide high power output (hundreds or even thousands of watts). But “rarely” doesn’t mean “never.”
图 4-23所示电路包含一个间接加热阴极的三极管。为了避免电路图过于复杂，我们省略了灯丝。在代表电子管外壳的圆圈内，阴极符号位于底部，控制栅极符号位于中间，阳极（或屏极）符号位于顶部。电子通常从阴极流向屏极，途中会经过控制栅极。控制栅极是一层金属丝网或屏蔽层，它会对电子的流动产生不同程度的干扰，干扰程度取决于在无信号输入条件下施加在其上的直流电压。
The circuit of Fig. 4-23 has a triode tube with an indirectly heated cathode. We omit the filament to keep the diagram from getting too messy. Within the circle that represents the tube envelope, the cathode symbol is at the bottom, the control grid symbol is in the middle, and the anode (or plate) symbol is at the top. Electrons flow generally from the cathode to the plate, passing through the control grid on the way. The control grid is a wire mesh or screen that interferes with the electrons to a greater or lesser extent, depending on the DC voltage that you place on it under no-signal conditions.
图 4-23 图 4-19和4-20中无线电报发射机的放大器电路原理图。这个“庞然大物”采用真空管，需要专用的高压（+600 V）直流电源。
FIG. 4-23 Schematic of the amplifier circuit in the radiotelegraph transmitter of Figs. 4-19 and 4-20. This “beast” employs a vacuum tube and needs a dedicated high-voltage (+600 V) DC power supply.
在大多数三极管放大器中，需要向控制栅极施加相对于阴极的负直流电压。可以通过使控制栅极电阻 R1 的阻值小于阴极电阻 R2 来实现该电压，从而使阴极相对于地（负电源电压的输入端）的电压高于控制栅极。随着 R1 相对于 R2 的阻值逐渐减小，负栅极偏置电压也会逐渐增大，控制栅极对电子流动的阻碍作用也会越来越强。
In most triode-tube amplifiers, you’ll supply the control grid with a negative DC voltage relative to the cathode. You can get that voltage by giving R1, the control-grid resistor, a smaller ohmic value than R2, the cathode resistor, thereby elevating the cathode farther above electrical ground (to which the negative power-supply voltage goes) than the control grid. As you increase the negative grid bias by making R1 progressively smaller with respect to R2, the control grid impedes the flow of electrons more and more.
在真空管射频功率放大器中，输入信号可以施加到控制栅极或阴极。在图 4-23的电路中，输入信号施加到控制栅极。这种布置方式使得放大器所需的输入功率远低于控制栅极接地且输入信号施加到阴极的情况。然而，当射频信号将阴极接地（这是电容 C2 的作用）并将输入信号施加到控制栅极时，控制栅极和阳极之间可能会产生意外振荡，从而导致杂散发射。这意味着麻烦！所谓的接地阴极电路，为了获得比接地栅极电路更高的增益和灵敏度，牺牲了稳定性。
In a vacuum-tube RF power amplifier, you can apply the input signal to the control grid or to the cathode. In the circuit of Fig. 4-23, the input signal goes to the control grid. That arrangement allows the amplifier to work with far less input power than it would need if the control grid were grounded and the input signal were applied to the cathode. However, when you ground the cathode for RF (that’s the function of C2) and apply the input signal to the control grid, you run the risk of unintended oscillation between the control grid and the plate. Then you get spurious emissions. That means trouble! In a so-called grounded-cathode circuit, you sacrifice stability in order to get greater gain and sensitivity than you could get with a grounded-grid circuit.
三种基本逻辑电路
Three Basic Logic Circuits
回顾第 3 章末尾关于逻辑门的章节。重新审视原理图符号（图 3-58）以及逻辑门如何处理输入以得出输出的描述（表 3-1）。
Look back at the section on logic gates at the end of Chapter 3. Reexamine the schematic symbols (Fig. 3-58) and the descriptions of how the logic gates process the inputs to derive the output (Table 3-1).
您可以将表 3-1分解为逻辑函数，其中 0 代表“假”（低电平），1 代表“真”（高电平）。工程师和逻辑学家将这种数组称为真值表。表 4-2至4-7将表 3-1中的文字描述重新表述为数值逻辑状态数组。
You can break Table 3-1 down into logic functions where 0 equals “falsity” (the low state) and 1 indicates “truth” (the high state). Engineers and logicians call such arrays truth tables. Tables 4-2 through 4-7 restate the verbal descriptions in Table 3-1 as arrays of numeric logic states.
让我们创建三个原理图，显示逻辑门的组合，并编制真值表，显示这些电路产生的逻辑状态。
Let’s create three schematic diagrams that show combinations of logic gates, and compile truth tables to show the logic states that those circuits produce.
表 4-2 逻辑非（NOT）真值表。
TABLE 4-2 Truth table for logical negation (NOT).
表 4-3 逻辑 OR 运算的真值表（含）。
TABLE 4-3 Truth table for the logical OR operation (inclusive).
表 4-4 逻辑与运算的真值表。
TABLE 4-4 Truth table for the logical AND operation.
表 4-5 逻辑 NOR 运算的真值表。
TABLE 4-5 Truth table for the logical NOR operation.
表 4-6 逻辑 NAND 运算的真值表。
TABLE 4-6 Truth table for the logical NAND operation.
表 4-7 逻辑 XOR 运算（异或）的真值表。
TABLE 4-7 Truth table for the logical XOR operation (exclusive OR).
案例1
Case 1
假设你将逻辑反相器（非门）与与门的两个输入端串联。图 4-24以示意图的形式展示了这种连接方式。输入端位于X点和Y点。我们指定并标记两个中间电路点为P 点和Q 点，并将输出点记为R点。在P点，条件为“非X ”。在Q点，条件为“非Y”。在R点，条件为“非Y ”。
Suppose that you place logical inverters (NOT gates) in series with both inputs of an AND gate. Figure 4-24 illustrates this arrangement as a schematic. The inputs appear at points X and Y. Let’s specify and label two intermediate circuit points as P and Q, and then call the output point R. At point P, you have the condition “NOT X.” At point Q, you have the condition “NOT Y.” At point R, you have the condition
（非X）且（非Y）
(NOT X) AND (NOT Y)
将每个点的所有可能逻辑状态汇总起来，即可得到表 4-8。该表显示了每个指定点在所有可能输入组合下的电路状态：
When you compile all the possible logic states at each of these points, you’ll get Table 4-8. This table shows the circuit condition at every point indicated for all possible input combinations:
• ( X , Y ) 5 (0,0)
• (X,Y) 5 (0,0)
• ( X , Y ) 5 (0,1)
• (X,Y) 5 (0,1)
• ( X , Y ) 5 (1,0)
• (X,Y) 5 (1,0)
• ( X , Y ) 5 (1,1)
• (X,Y) 5 (1,1)
图 4-24 逻辑反相器与 AND 门的两个输入端串联。
FIG. 4-24 Logical inverters in series with both inputs of an AND gate.
表 4-8 图 4-24逻辑电路的真值表。
TABLE 4-8 Truth table for the logic circuit of Fig. 4-24.
案例 2
Case 2
假设在异或门 (XOR) 后接一个反相器 (VERSOR)。图 4-25以示意图的形式展示了这一系列逻辑门。和之前一样，我们称输入点为X和Y。在点P，有“ X NOR Y ”的逻辑状态，当点X和Y 的逻辑状态相反时，该状态为高电平；当点X和Y 的逻辑状态相同时，该状态为低电平。在点Q ，有输出状态，该状态始终与点P 的状态相反。表 4-9列出了所有可能的输入组合下，点X、Y、P和Q的逻辑状态：
Suppose that you follow an XOR gate with an inverter. Figure 4-25 shows this sequence of logic gates in schematic form. As before, let’s call the input points X and Y. At point P, you have the condition “X NOR Y,” which is high when points X and Y have opposite logic states, and low when points X and Y have the same logic state. At point Q, you have the output state, which is always the opposite of the state at point P. Table 4-9 depicts the logic states at points X, Y, P, and Q for all possible input combinations:
• ( X , Y ) 5 (0,0)
• (X,Y) 5 (0,0)
• ( X , Y ) 5 (0,1)
• (X,Y) 5 (0,1)
• ( X , Y ) 5 (1,0)
• (X,Y) 5 (1,0)
• ( X , Y ) 5 (1,1)
• (X,Y) 5 (1,1)
图 4-25 异或门后接逻辑反相器。
FIG. 4-25 An XOR gate followed by a logical inverter.
表 4-9 图 4-25的逻辑电路的真值表。
TABLE 4-9 Truth table for the logic circuit of Fig. 4-25.
案例3
Case 3
假设你将一个反相器与异或门的每个输入端串联。图 4-26是这种连接的示意图。在P点，条件为“非X ”。在Q点，条件为“非Y ”。在R点，条件为……
Suppose that you place an inverter in series with each input of an XOR gate. Figure 4-26 is a schematic of this arrangement. At point P, you have the condition “NOT X.” At point Q, you have the condition “NOT Y.” At point R, you have the condition
（非X）异或（非Y）
(NOT X) XOR (NOT Y)
表 4-10列出了该电路中所有可能的逻辑状态。同样，存在四种可能的输入组合，您必须仔细观察每种输入组合下信号在电路中传播时发生的情况：
Table 4-10 breaks down all possible logic states in this circuit. Once again, four possible input combinations exist, and you must scrutinize what happens as the signals make their way through the circuit for each input combination:
• ( X , Y ) 5 (0,0)
• (X,Y) 5 (0,0)
• ( X , Y ) 5 (0,1)
• (X,Y) 5 (0,1)
• ( X , Y ) 5 (1,0)
• (X,Y) 5 (1,0)
• ( X , Y ) 5 (1,1)
• (X,Y) 5 (1,1)
图 4-26 逻辑反相器与 XOR 门的两个输入端串联。
FIG. 4-26 Logical inverters in series with both inputs of an XOR gate.
表 4-10 图 4-26逻辑电路的真值表。
TABLE 4-10 Truth table for the logic circuit of Fig. 4-26.
概括
Summary
本章旨在提升你的电路图阅读能力，使你能够阅读展示电路组装方式的电路图，或根据已知的电路细节绘制电路图。经过更多练习后，你应该能够轻松查看简单的电路原理图并想象出最终的电路。你甚至可能对如何在电路板上排列元件有所了解，即使电路原理图并未明确说明具体操作方法。
This chapter has given give you some diagram-reading expertise, so you can read diagrams that show how circuits get assembled, or draw diagrams on the basis of known circuit details. After some more practice, you should have no trouble viewing a simple schematic and visualizing the finished circuit. You might even get an idea of how to arrange the components on a circuit board, even though schematics don’t explicitly tell you how to do that.
假以时日，你会“逐渐接受”示意图符号；它会演变成一种新的语言，你最终会学会用这种语言思考，就像你可以通过经常使用文字、数学方程式、乐谱、建筑蓝图、摩尔斯电码或任何其他语言来思考一样。
Given time, schematic symbology will “grow on you”; it’ll evolve into a new language in which you’ll eventually learn to think, just as you can think in terms of words, mathematical equations, musical scores, architectural blueprints, Morse code, or any other language if you use those tools regularly and often.
5
5
复杂电路
Complex Circuits
在学习阅读和绘制电路图的过程中，不要因为偶尔遇到的困难而气馁。你可能会想：“任何人都能学会阅读简单电路的原理图，比如只有一两个晶体管、几个电容器和几个电阻器的电路。但要解读复杂的电路图，恐怕需要好几年时间。” 事实并非如此！学习过程中固然需要付出一些努力，但你总能将复杂的系统分解成简单的电路。
As you learn to read and draw schematic diagrams, don’t get discouraged by occasional difficulties. You might think, “Anyone can learn to read schematics of simple circuits, like those that have a transistor or two, a few capacitors, and a few resistors. But it’ll take years before I can decipher complex schematics.” Not so! You must put some effort into the learning process, but you can always break a complicated system down into simple circuits.
识别基本组成部分
Identifying the Building Blocks
即使乍看之下系统图复杂得令人眼花缭乱，它实际上也只是由许多以简单方式相互连接的小型电路组成。一个包含六个二极管、十个电感器、十个晶体管以及数十个电阻器和电容器的系统，可以分解成四五个简单的电路，每个电路只包含几个元件。如果你一下子看完整个系统原理图，就好比试图一口气吃下一个巨型汉堡。就像吃汉堡一样，把原理图分成小块来理解，会更容易掌握。
Even a system whose diagram looks overwhelming at first glance comprises smaller circuits interconnected in a straightforward way. A system with six diodes, ten inductors, ten transistors, and dozens of resistors and capacitors might resolve into four or five simple circuits, each containing only a few components. If you look at the entire system schematic all at once, you might as well try to eat a jumbo hamburger in a single swallow. With the diagram, as with the burger, you face an easier task if you assimilate the thing in little bites or pieces.
图 5-1展示了一个由天线、抽头式空芯电感器、可变电容器、射频二极管和固定电容器构成的“晶体收音机”接收机。“晶体”一词源于 20 世纪初射频二极管的原始构造。为了使单向电流门能够作为信号检测器（或解调器），无线电实验者将一根被称为“猫须”的细导线与一块被称为方铅矿的结晶硫化铅接触。如今，半导体二极管处理射频信号的方式与曾经的“晶体”相同，尽管现代射频二极管的外观与古老的方铅矿和“猫须”装置截然不同。
Figure 5-1 shows a “crystal radio” receiver built with an antenna, a tapped air-core inductor, a variable capacitor, an RF diode, and a fixed capacitor. The term “crystal” derives from the original construction of RF diodes in the early 1900s. In order to get a one-way current gate to act as a signal detector (or demodulator), radio experimenters placed a strand of fine wire called a cat’s whisker into contact with a chunk of crystalline lead sulfide called galena. Today, semiconductor diodes process RF signals in the same way as “crystals” once did, even though modern RF diodes don’t look like the old galena-and-cat’s-whisker contrivances.
图 5-1 为“晶体收音机”接收机的调谐电路和检波器级示意图。该电路产生微弱的音频信号。
FIG. 5-1 Schematic of the tuned circuit and detector stages of a “crystal radio” receiver. This circuit produces a weak audio-frequency (AF) signal.
图 5-1的电路不能称之为“复杂”，但它确实实现了一些精妙的功能。除了天线（例如从窗框下方延伸到树上的外部元件）和一个灵敏的传感器之外，该电路还包含其他组件。您可以连接耳机或耳麦到输出端来收听广播电台（即使声音很微弱），该电路仅包含四个元件：线圈、二极管和两个电容器。
You can’t call the circuit of Fig. 5-1 “complicated,” but it performs some sophisticated tricks. Aside from the antenna (an external component such as a length of wire running outdoors under a window sash to a tree) and a sensitive earphone or headphone that you can connect at the output terminals to hear radio stations (however faintly), this circuit contains only four components: the coil, the diode, and two capacitors.
您可以将放大器连接到“矿石收音机”的输出端，以增强音频频率(AF) 的音量，使其足以驱动耳机达到舒适的聆听音量。图 5-1中输出端未显示耳机。要实现这一点，您需要另一个电路，以及电池或其他直流电源，以使音频输出信号足够强。
You can connect an amplifier to the output of the “crystal radio” to boost the audio-frequency (AF) volume to the point where it can drive a headset to a comfortable listening level. Figure 5-1 doesn’t include a headset at the output. To accomplish that feat, you’ll need another circuit, along with a battery or other source of DC power to make the AF output signal strong enough.
图 5-2展示了另一个相当简单的电路图：一个采用单个 NPN 双极型晶体管的音频放大器。除了晶体管之外，该电路还包含四个电阻和三个电容，总共八个元件。它需要一个直流电源，例如电池（图中未显示），提供 12V 电压。该电路的输入端接收一个低电平音频信号（例如，来自“矿石收音机”的输出），并将信号放大到足以让耳机发出声音的水平。经验丰富的工程师可能只需几分钟就能画出电路图，但需要几个小时来搭建和测试电路，并不断调整元件参数以获得最佳性能。
Figure 5-2 shows another fairly simple schematic: an AF amplifier that employs a single NPN bipolar transistor. In addition to the transistor, this circuit has four resistors and three capacitors for a total of eight components. It needs a source of DC power such as a battery (not shown), which provides 12 V. This circuit accepts a low-level AF signal (the output of a “crystal radio,” for example) at the input terminals and boosts the power to a level strong enough to make audible sound come out of a headset. An experienced engineer might need a couple minutes to scribble the schematic and a couple of hours to build and test the circuit, “tweaking” the component values to get the best possible performance.
图 5-2 一个 AF 前置放大器电路，可以与“晶体收音机”配合使用，产生足以驱动耳机的强信号。
FIG. 5-2 An AF preamplifier circuit that can work with the “crystal radio” to produce a signal strong enough to drive a headset.
图 5-2所示电路接收微弱信号并将其放大到合理（但功率不大）的水平，因此有时被称为前置放大器。如果您想驱动扬声器，使教室里的所有学生都能听到声音，则需要更大的放大倍数。您可以通过在前置放大器的输出端连接一个或多个额外的放大器来获得额外的音频放大。
Because the circuit of Fig. 5-2 takes a weak signal and boosts it to a reasonable (but not very powerful) level, it’s sometimes called a preamplifier. If you want to drive a speaker so that all the students in a classroom can hear the sound, you’ll need more amplification. You can get that extra AF boost with one or more additional amplifiers connected to the output of the preamplifier.
图 5-3是一个电路原理图，乍一看似乎比图 5-1或图 5-2都复杂。但仔细观察图 5-3后，你会发现它其实就是“矿石收音机”（图 5-1）和音频前置放大器（图 5-2）的组合。元件编号大致按照从左到右的顺序排列，与信号在系统中的流动方向一致。（在同一电路原理图中，元件编号绝不能重复。）在图 5-3中，原始电路的连接方式如下：“矿石收音机”和前置放大器对应于从 C2 上方的点到 C3 左侧的短水平线。
Figure 5-3 is a schematic of a circuit that looks, at first glance, more complicated than either Fig. 5-1 or Fig. 5-2. But as you examine Fig. 5-3 for a minute, you’ll see that it’s nothing more than the composite of the “crystal radio” (Fig. 5-1) and the AF preamplifier (Fig. 5-2). The components are re-numbered generally going from left to right, the direction of signal flow through the system. (You should never duplicate a component designator within a single schematic.) In Fig. 5-3, the connection between the original “crystal radio” and the preamplifier corresponds to the short, horizontal line that goes from the dot above C2 to the left-hand side of C3.
图 5-3 “晶体收音机”调谐电路、检波器和音频前置放大器级的组合。部分元件标识与图 5-2相比有所更新。
FIG. 5-3 Combination of “crystal radio” tuned circuit, detector, and AF preamplifier stages. Some component designators are updated from Fig. 5-2.
现在您已经能够想象出图 5-3 所示电路的两个基本组成部分，整个电路图看起来是不是很简单？您可以追踪信号如何依次经过“晶体收音机”和音频前置放大器。从射频信号到达天线到音频信号出现在输出端，整个过程仅需极短的时间。
Now that you can envision the two building blocks that make up the circuit of Fig. 5-3, the whole diagram looks elementary, wouldn’t you say? You can follow the signal as it passes through the “crystal radio” and then through the AF preamplifier. The entire process, from the RF signal arriving at the antenna to the AF energy appearing at the output, takes place in a tiny fraction of a second.
图 5-3所示电路产生的信号强度比仅依靠天线射频电流供电的“矿石收音机”微弱输出要强得多。然而，即使是图 5-3所示电路放大后的音频输出，其音量也不足以让扬声器提供舒适的聆听体验。连接耳机后，它能提供一定的音量，但并不大。为了进一步提升音频信号强度，您需要一个功率更大的放大器。
The circuit of Fig. 5-3 produces a stronger signal than the feeble output of the “crystal radio” alone, which gets its power only from RF current that flows in the antenna. Nevertheless, even the amplified AF output from the circuit of Fig. 5-3 isn’t strong enough to provide a comfortable listening volume in a loudspeaker. It offers some sound power if you connect a headset to it, but not much. In order to further boost the AF signal level, you’ll need a substantial power amplifier.
图 5-4显示了一个能够产生可观声功率的双晶体管电路。它被称为推挽放大器。上面的晶体管放大音频波形的一半，下面的晶体管放大另一半。想象一下，Q1 负责“推”，Q2 负责“拉”，所以当你将它们的输出组合起来时，你会得到一个整个输入波形的放大版本。推挽放大器可以接收来自低电平放大器（例如图 5-3所示电路）的微弱音频信号，并将其放大到足以使扬声器发出响亮的声音！
Figure 5-4 shows a two-transistor ensemble that can produce respectable sound power. It’s called a push-pull amplifier. The top transistor amplifies half the AF waveform and the bottom transistor amplifies the other half. Imagine that Q1 “pushes” and Q2 “pulls” so when you combine their outputs, you get a magnified version of the entire input waveform. The push-pull amplifier can take the weak AF signal from a low-level amplifier (such as the circuit of Fig. 5-3) and boost it enough to make some loud sound come out of a speaker!
图 5-4 适用于驱动扬声器的 AF 功率放大器电路。
FIG. 5-4 An AF power amplifier circuit suitable for driving a speaker.
如果输入信号功率不足，图 5-4所示电路将无法获得足够的驱动力（输入功率）来产生合适的输出信号。图 5-3所示电路（音频前置放大器）可以提供足够的功率来充分驱动推挽式音频功率放大器，例如图 5-4所示的放大器。而图 5-1所示电路（单独的“矿石收音机”）则无法做到这一点。
If the input signal doesn’t contain much power, then the circuit of Fig. 5-4 won’t get enough drive (input power) to produce a decent output signal. The circuit of Fig. 5-3 (the AF preamplifier) can provide enough “oomph” to adequately drive a push-pull AF power amplifier such as the one diagrammed in Fig. 5-4. The circuit of Fig. 5-1 (the “crystal radio” alone) can’t.
如果将图 5-3和图5-4中的电路级联（一个接一个），就能得到一个完整的 AM 收音机，并能通过扬声器发出不错的声音。图 5-5以单张电路图的形式展示了整个三晶体管 AM 收音机。同样，我们修改了之前电路图中出现的一些元件编号，因此从天线输入端到扬声器输出端，元件编号通常会递增，并且我们特意避免将两个不同的元件命名为相同的名称。
If you combine the circuits of Figs. 5-3 and 5-4 in cascade (one after the other), you get a complete AM radio receiver that will produce respectable sound from a speaker. Figure 5-5 shows the entire three-transistor AM radio receiver in a single schematic. Again, we’ve had to change some of the component designators that appeared in previous diagrams, so they increase generally as you go from the original input at the antenna to the final output at the speaker, taking pains to ensure that you don’t inadvertently give two different components the same name.
图 5-5 完整的收音机接收电路。音频功率放大器级中的一些元件标识与图 5-4相比有所更新。此原理图包含扬声器。
FIG. 5-5 Complete radio receiver circuit. Some of the component designators in the AF power amplifier stage are updated from Fig. 5-4. This schematic includes the speaker.
电子系统的演化可以分解为一个明确的步骤。首先，各个元件（电阻器、电容器、二极管等）组合成简单的电路。其次，这些简单的电路组合成复杂的器件，在某些情况下，甚至构成整个系统。最后，如果设计足够复杂，这些复杂的电路最终组合成完整的系统。
The evolution of an electronic system breaks down into a well-defined sequence. First, the individual components (resistors, capacitors, diodes, and so on) combine to form simple circuits. Second, those simple circuits combine to make complex devices or, in some cases, the whole system. Third, if the design is sophisticated, the complex circuits combine to form the complete system.
几种不同的设备（有些很简单，有些则不然）可以组合成一个大型系统。业余无线电台就是一个很好的例子。它可能包含收发器（发射机/接收机一体机）、天线调谐器、个人电脑、连接电脑和收发器的接口单元、用于发射语音信号的麦克风、连接麦克风和收发器的语音处理器以及一个按键。 它允许你根据需要使用摩尔斯电码进行传输，还配有耳机、扬声器和电源，可以将市电交流电转换为直流电，整个系统从直流电中获得运行所需的各种形式的电力。
Several different devices (some of them simple and others not so simple) can combine to form a large system. An amateur radio station offers a good example. It might have a transceiver (transmitter/receiver in a single box), an antenna tuner, a personal computer, an interface unit that goes between the computer and the transceiver, a microphone that lets you transmit voice signals, a speech processor that goes between the microphone and the transceiver, a key that lets you transmit in Morse code if you want, a headset, a speaker, and a power supply that converts utility AC into the DC from which the whole system gets the various forms of electricity that it needs in order to function.
分页符
Page Breaks
图 5-5是一个“相当复杂”的示意图。你可以用两层结构来绘制这个系统，探测器和前置放大器位于上层，音频功率放大器位于下层。一条长长的弯曲线，中间被 C5 断开，代表前置放大器输出和功率放大器输入之间的连接。从技术角度来说，这个示意图并没有什么问题，但有些人更喜欢把所有电路都放在同一层上。为了实现这一点，你可以把示意图缩小很多，或者横向绘制在页面上。你甚至可以把它做成折页（就像那些高档印刷杂志为了展示精彩内容而采用的那种做法）。
Figure 5-5 is a “respectably complicated” diagram. You can draw the system in a two-level format with the detector and preamplifier on top, and the audio power amplifier on the bottom. A long, tortuous line, broken in the middle by C5, represents the connection between the preamplifier output and the power amplifier input. There’s nothing technically wrong with this diagram, but some people would rather see it all on one level. In order to render the diagram that way, you could make it extremely small, or else draw it sideways on the page. You could even produce it on a foldout page (the sort of thing that they do in those upscale print magazines when they want to show you something spectacular).
不过，您还有另一种选择！您可以将电路图分成多页。对于图 5-5的原理图，您无需使用这种方法，但对于业余无线电收发器、电视机或计算机等极其复杂的系统，您可能需要利用这种方法。图 5-6展示了如何将此技术应用于图 5-5中的无线电接收机电路图。图 5-6A将调谐器、检波器和音频前置放大器正面朝上地放在同一页上，输出指示器显示为一个指向右侧页面外的箭头内的 X。图 5-6B显示了推挽式音频功率放大器，其输入指示器由一个指向左侧页面外的箭头内的 X 组成。
You have yet another alternative, though! You can split the diagram into multiple pages. You need not use that approach with the schematic of Fig. 5-5, but when you get to extremely complicated systems such as amateur radio transceivers, television sets, or computers, you might want to take advantage of that option. Figure 5-6 shows how you can use this technique with the diagram of the radio receiver from Fig. 5-5. Figure 5-6A puts the tuner, detector, and AF preamplifier right-side-up on a single page along with an output designator that appears as an X inside an arrow that points off the page toward the right. Figure 5-6B shows the push-pull AF power amplifier with an input designator comprising an X inside an arrow that points off the page toward the left.
图 5-6A 为收音机接收机中的调谐器、检波器和音频前置放大器级。楔形 X 表示图 B 的延伸部分。
FIG. 5-6A Tuner, detector, and AF preamplifier stages in the radio receiver. The wedge X represents an extension to drawing B.
图 5-6B 收音机接收机中的音频功率放大器和扬声器。楔形 X 表示图 A 的延伸部分。
FIG. 5-6B The AF power amplifier and speaker in the radio receiver. The wedge X represents an extension from drawing A.
让我们沿着图 5-6A中的信号路径来分析。自由空间中的无线电波会使射频电流流经天线以及电感 L1。电容 C1 使电感/电容组合（称为LC 电路，其中斜体L代表“电感”，斜体C代表“电容”）在您想要收听的射频信号频率处谐振。二极管 D1 检测（解调）信号，将其中的音频 (AF) 部分和射频 (RF) 部分分离。电容 C3 将该信号的音频部分传递到晶体管 Q1 的基极。电容 C2 将二极管输出端的射频部分短路到地，因为电路不再需要射频能量；事实上，它的存在可能会在后续电路中造成问题！晶体管 Q1 在其基极处对微弱的音频信号进行放大。电阻 R1、R2、R3 和 R4 确保 Q1 获得最佳直流电压（称为偏置），从而使其产生最大的音频增益。电容 C4 将发射极保持在音频信号地，同时允许其存在少量直流电压。音频输出信号以及来自电源的部分直流电压（+12V）通过标有 X 的向右箭头输出到纸外。
Let’s follow the signal through Fig. 5-6A. A radio wave in free space causes RF current to flow in the antenna, and also through inductor L1. Capacitor C1 causes the inductor/capacitor combination (called an LC circuit, where an italic L stands for “inductance” and an italic C stands for “capacitance”) to resonate at the frequency of the RF signal that you want to hear. Diode D1 detects (demodulates) the signal, splitting the AF and RF portions apart. Capacitor C3 passes the AF portion of that signal along to the base of transistor Q1. Capacitor C2 shunts (short-circuits) the RF portion of the diode’s output to ground, because the circuit doesn’t need the RF energy anymore; its presence could, in fact, cause trouble in the following stages! Transistor Q1 acts as an amplifier for the weak AF signal at its base. Resistors R1, R2, R3, and R4 ensure that Q1 gets optimum DC voltage (called bias), so that it will produce the greatest possible AF gain. Capacitor C4 keeps the emitter at AF signal ground while allowing some DC voltage to exist there. The AF output signal, along with some DC from the power supply (+12 V), goes off the page through the rightward-pointing arrow marked X.
现在我们来看一下图 5-6B ，并追踪从图 5-6A输入的信号。音频信号能量以及一些直流分量出现在标有 X 的向左箭头处。电容器 C5 阻隔了直流分量，因此只有音频电流可以到达电位器 R8。
Now let’s look at Fig. 5-6B and follow the signal after it comes in from Fig. 5-6A. The AF energy, along with some DC, appears at the leftward-pointing arrow marked X. Capacitor C5 blocks the DC so that only the AF current can reach potentiometer R8.
完整的音频电压会出现在电阻 R8 的整个电阻两端。箭头指向锯齿形，表示电位器的滑动触点，它“拾取”的音频电压范围从零（一直到锯齿形的右端，接地）到最大值（一直到锯齿形的左端，电容 C5）。滑动触点的信号会使音频电流流过变压器 T1 的初级线圈。然后，信号的流动路径与图 5-4 中的“追踪信号流”部分所述相同。此情况与图 5-4的唯一区别在于元件编号。您还可以像图 5-5中那样，在 T2 的输出端添加一个扬声器。
The full AF voltage appears across the entire resistance of R8. The arrow touching the zig-zag symbolizes the potentiometer wiper or slider, which “picks off” AF voltages that can range from zero (all the way to the right-hand end of the zig-zag, at ground) to the maximum possible (all the way to the left-hand end of the zig-zag, at C5). The slider signal causes AF current to flow in the primary of transformer T1. From there, the signal flows as described in “Follow the flow” for Fig. 5-4. The only difference between this situation and that one is the numbering of the component designators. You can also add a speaker to the output of T2, as you did in Fig. 5-5.
更多电路
Some More Circuits
图 5-7显示了一个称为L 型网络的天线匹配电路。这里的字母 L 指的是图中元件的总体布局，而不是电路中的电感器。（实际上，要使图 5-7中的线圈和电容器在布局中呈现大写字母 L 的形状，您需要将页面顺时针旋转 90 度，然后对着镜子观察！但您应该明白我的意思了吧？）
Figure 5-7 shows an antenna matching circuit known as an L network. In this case, the letter L refers to the general layout of the components in the diagram, not to the inductor in the circuit. (Actually, to make the coil and capacitor in Fig. 5-7 take the shape of an uppercase L in the layout, you’ll have to rotate the page 90 degrees clockwise and then hold it up to a mirror! But you get the general idea, right?)
图 5-7 由电感器和可变电容器组成的 L 网络。
FIG. 5-7 An L network comprising an inductor and a variable capacitor.
图 5-8显示了另一种天线匹配网络，它是在图 5-7 的电路基础上，在输入端增加了一个额外的电容器。工程师们将这种电路称为π 网络，因为其元件在原理图中的形状类似于大写希腊字母 π。
Figure 5-8 shows another type of antenna matching network, which comprises the circuit from Fig. 5-7 with an extra capacitor added at the input end. Engineers call this type of circuit a pi network because its components, in the schematic layout, resemble the shape of the upper case Greek letter pi (π).
图 5-8 由一个电感器和两个可变电容器组成的π型网络。
FIG. 5-8 A pi network comprising an inductor and two variable capacitors.
图 5-9所示的电路比图 5-7和图5-8中的电路更复杂，但某种程度上又包含了它们的组合。将一个 π 型网络与一个 L 型网络连接起来，就得到了一个π-L 型网络。与前两个图中的电路相比，图 5-9所示电路的优势在于，它能够使射频发射器与原本无法接收功率的天线配合工作。这两个额外的元件可以发挥巨大的作用！
Figure 5-9 shows a circuit that’s more complicated than the ones in Figs. 5-7 and 5-8, but in a sense contains them both put together. When you follow a pi network with an L network, you get a pi-L network. The advantage of a circuit like the one in Fig. 5-9, compared to those in the previous two diagrams, lies in its ability to make RF transmitters work with antennas that otherwise wouldn’t accept power. Those two extra components can go a long way!
图 5-9 由两个电感器和三个可变电容器组成的 pi-L 网络。
FIG. 5-9 A pi-L network comprising two inductors and three variable capacitors.
如果你年纪够大，应该还记得以前想考取业余无线电操作员执照就必须学习国际莫尔斯电码（通常简称“电码”）。这项规定如今已成为历史，但一些业余无线电爱好者仍然喜欢用这种方式进行通信。如果你也想这样做，就必须学会“读”和“说”电码。为此，你可以制作一个电码练习振荡器，例如图 5-10中所示的振荡器。这是一个音频振荡器，可以用一个直键或电报键来控制它的开关，图中标记为“键”。（由于电报键本质上是一个单刀单掷开关，你可以将其标记为 S1。）
If you’re old enough, you’ll remember the days when you had to learn the International Morse code (often simply called “the code”) to get an amateur radio operator’s license. That mandate has passed into history, but some amateur radio operators still enjoy communicating this way. If you want to do that, you must learn to “read” and “speak” in the code. To that end, you can build a code practice oscillator such as the one diagrammed in Fig. 5-10. It’s an AF oscillator that you can switch on and off with a straight key or telegraph key, labeled “Key” in the figure. (Because a telegraph key technically constitutes an SPST switch, you could label it S1.)
图 5-10 一个使用两个 PNP 双极型晶体管的音频编码练习振荡器。Rx 和 Cx 的值决定了频率。
FIG. 5-10 An AF code-practice oscillator using two PNP bipolar transistors. The values of Rx and Cx determine the frequency.
当你第一次查看图 5-10 时，你可能会疑惑为什么一个音频振荡器电路需要这么多元件。难道不能像前面讨论过的前置放大器或功率放大器那样，构建一个简单的音频放大器，然后将部分输出馈入电路吗？回到输入端？当然可以；但是，如果你想让你的代码练习振荡器发出悦耳的“音调”，使用图 5-10所示的电路会获得更好的效果。它被称为双 T 型振荡器，因为其电路呈 T 形，包括标记为 Rx 的电阻和标记为 Cx 的电容。双 T 型振荡器可以产生悦耳动听、音调（频率）稳定且可预测的音符。
When you first examine Fig. 5-10, you might wonder why an AF oscillator circuit needs so many components. Can’t you build a simple AF amplifier like the preamplifier or power amplifier discussed earlier, and feed some of the output back to the input? Well, yes, you can do that; but if you want a decent “tone” to come out of your code practice oscillator, you’ll get superior results with a circuit like the one in Fig. 5-10. It’s called a twin-T oscillator because of the T-shaped configurations including the resistors marked Rx and the capacitors marked Cx. The twin-T oscillator produces a musical note that’s pleasing to the ears and has a predictable and stable pitch (frequency).
图 5-10所示电路使用 9V 电池作为电源。在本例中，晶体管为 PNP 型，因此其集电极带负电压，电池正极直接接地。因此，该电路构成一个正极接地系统。
The circuit of Fig. 5-10 uses a 9-V battery as its power source. In this example, the transistors are of the PNP type, so the collectors get a negative voltage while the positive battery terminal goes straight to ground. This circuit therefore constitutes a positive-ground system.
您可能希望使用交流市电而非电池来构建电源。如果是这样，您需要设计一个能够产生相对于地为负电压的电源。图 5-11显示了一个可以提供纯净、恒定的 -9VDC 电压的电源。它与您在图 4-13中看到的电路几乎相同，但有以下几点不同：
You might want to build a power supply from the AC utility mains rather than relying on a battery. If you want to do that, you’ll need to design the supply so that it produces a negative voltage with respect to ground. Figure 5-11 shows a power supply that can provide pure, constant –9VDC. It’s almost the same circuit as the one you saw back in Fig. 4-13, with the following exceptions:
图 5-11 为一个稳压 -9 VDC 电源，可为 图 5-10中的编码练习振荡器供电。注意正极接地，以便与 PNP 晶体管一起使用。
FIG. 5-11 A regulated –9 VDC power supply that can power the code-practice oscillator of Fig. 5-10. Note the positive ground for use with PNP transistors.
• 所有二极管都反向工作（包括齐纳二极管）。
• All the diodes go in the opposite direction (including the Zener diode).
• 电解电容器的极性相反。
• The electrolytic capacitor has the opposite polarity.
• 该电路产生较低的直流输出电压。
• The circuit produces a lower DC output voltage.
图 5-12显示了一个完整的音频编码练习振荡器系统，该系统可使用交流电源供电。它将图 5-11的电源与图 5-10的振荡器组合在一起。与图 5-5的无线电接收机原理图类似，您需要用一根导线（但长度比图 5-5中的导线短）将图 5-12中的电源输出连接到振荡器。图 5-12还显示了一个音量控制旋钮 (R6) 和一副耳机。
Figure 5-12 shows a complete AF code practice oscillator system that can operate from the AC utility mains. It combines the power supply of Fig. 5-11 with the oscillator of Fig. 5-10. As with the radio receiver schematic of Fig. 5-5, you connect the power supply output to the oscillator in Fig. 5-12 with a single line (but not as long as the one in Fig. 5-5). Figure 5-12 also shows a volume control (R6) and a pair of headphones.
图 5-12 稳压电源和编码练习振荡器的组合。请注意新增的音量控制和耳机接口。
FIG. 5-12 Combination of the regulated power supply and code practice oscillator. Note the addition of the volume control and headphones.
您可能需要提升双T振荡器的输出功率，以便音频功率能够驱动扬声器，从而向满教室的学生发送莫尔斯电码！一个推挽式音频放大器（例如您用于收音机的放大器，只是用PNP晶体管代替NPN晶体管）就能完成这项工作。这样，您就得到了一个包含三个基本电路的系统：电源、振荡器和放大器。图5-13A、B和C显示了完整的系统原理图，分布在三页上。
You might want to boost the twin-T oscillator output so that the AF power will drive a loudspeaker, letting you send Morse code to a classroom full of students! A push-pull AF amplifier, such as the one you used for the radio receiver except with PNP rather than NPN transistors, will do this job. Then you’ll get a system with three essential circuits: a power supply, an oscillator, and an amplifier. Figures 5-13A, B, and C show the complete system schematic spread across three different pages.
图 5-13A 用于课堂编程练习系统的稳压电源。楔形 X 表示图 B 和图 C 的延伸部分。
FIG. 5-13A A regulated power supply for a classroom code-practice system. The wedge X represents an extension to illustrations B and C.
图 5-13B 用于课堂编程练习系统的双 T 型音频振荡器。楔形 X 表示上一页图 A 的延伸部分。楔形 Y 表示图 C 的延伸部分。
FIG. 5-13B A twin-T audio oscillator for a classroom code-practice system. The wedge X represents an extension from illustration A on the previous page. The wedge Y represents an extension to illustration C.
图 5-13C 用于课堂编程练习系统的音频功率放大器。请注意图中的 PNP 晶体管，这与负电源电压（正地系统）一致。楔形 X 表示上一页图 A 的延伸部分。楔形 Y 表示图 B 的延伸部分。
FIG. 5-13C An AF power amplifier for a classroom code-practice system. Note the PNP transistors, consistent with the negative power-supply voltage (positive-ground system). The wedge X represents an extension from illustration A on the previous page. The wedge Y represents an extension from illustration B.
图 5-14展示了一个简单的 LC 电路，它类似于图 5-7中的 L 型网络，但电感和电容的位置互换了，电容是固定的而不是可变的，电感器采用的是粉末冶金磁芯而不是空心磁芯。此外，该电路的功能也与图 5-7 中的电路不同。图 5-7中的电路主要用于调谐天线系统或使发射机的输出与特定天线匹配。图 5-14中的电路则根据信号的频率来控制信号的通过（或阻断）。它被称为高通滤波器，因为随着频率的增加，它允许信号更容易通过。高衰减（信号损耗大）转变为低衰减（信号损耗小或无信号损耗）的确切频率取决于电容和电感的值。
Figure 5-14 shows a simple LC circuit that resembles the L network of Fig. 5-7, but the inductor and capacitor have changed places, the capacitor is fixed rather than variable, and the inductor has a powdered-iron core instead of an air core. In addition, this circuit performs a different function than the other one does. The circuit in Fig. 5-7 works mainly to tune an antenna system or to match the output of a transmitter to a particular antenna. The circuit in Fig. 5-14 is designed to let signals get through (or not) depending on their frequency. It’s called a highpass filter because it lets signals pass more easily as the frequency increases. The exact frequency at which high attenuation (lots of signal loss) changes to low attenuation (little or no signal loss) depends on the values of the capacitor and inductor.
图 5-14 一个简单的频率敏感滤波器电路。
FIG. 5-14 A simple frequency-sensitive filter circuit.
图 5-15显示了一个更复杂的 LC 电路，它由两个级联滤波器组成。第一个滤波器由串联电容 C1 和并联电感 L1 构成，其设计与图 5-14中的滤波器相同。第二个滤波器由串联电感 L2 和并联电容 C2 构成，是一个低通滤波器。它的工作原理与高通滤波器相反，频率越低，信号越容易通过。
Figure 5-15 shows a more complicated LC circuit that comprises two filters in cascade. The first filter, made up of the series-connected capacitor C1 and the parallel-connected inductor L1, has the same design as the one in Fig. 5-14. The second filter, made up of the series-connected inductor L2 and the parallel-connected capacitor C2, forms a lowpass filter. It works in the opposite manner from a highpass filter, letting signals get through more easily as the frequency goes down.
图 5-15 一种复杂的频率敏感滤波器，由两个简单但不同的滤波器级联而成。
FIG. 5-15 A complex frequency-sensitive filter comprising two simple, but different, filters connected in cascade.
当一个高通滤波器之后紧跟一个低通滤波器，并且你选择的截止频率（或过渡点）使得高通滤波器的截止频率低于低通滤波器的截止频率时，就得到了一个带通滤波器。当信号频率位于两个截止频率之间时，信号可以轻松通过该滤波器。如果信号频率位于“易通过区”之外，则会被大幅衰减。
When you follow a highpass filter with a lowpass filter, and if you choose the cutoff frequencies (or transition points) so that the highpass filter cutoff frequency lies below the lowpass filter cutoff frequency, you get a bandpass filter, which a signal can pass through easily when its frequency lies between the two cutoffs. If the frequency lies outside the “zone of easy passage,” it gets greatly attenuated.
如果你了解一个循环系统中某个电路的工作原理，那么你也就间接地了解了所有电路的工作原理。一个电路出现的问题也可能出现在其他电路中。例如，假设你通过测试发现，一个振荡器的频率变化是由于基极电路中的一个电阻损坏造成的。如果另一个配置相同的振荡器也出现同样的故障，你可以查看电路图，找到第二个基极电阻，并进行一些测试，看看它是否也损坏了。如果没有电路图，你将很难找到这个故障电阻。
If you know how one of the circuits in a repetitive system operates, then you know, by extension, how all the circuits work. A problem that develops in one circuit might also arise in any of the others. For example, suppose that you learn (by testing) that an oscillator has changed frequency because of a defective resistor in the base circuit. If another oscillator of the same configuration develops the same malfunction, you can consult the schematic, locate the second base resistor, and conduct some tests to see if it, too, has gone bad. Without the schematic, you’d have a difficult time locating the rogue resistor.
如果将一个庞大的故障系统分解成多个复杂的电路，就能找出哪个电路可能是罪魁祸首。然后，可以将这个复杂的电路进一步拆分成简单的电路，最终确定哪个电路最有可能出问题。在这个故障电路中，可以逐个检查各个元件。如果借助电路图进行这样的排除法，就能比没有电路图时更轻松地修复设备。工程师通常会把这种故障排除过程称为“元件级故障排除”。
If you break a gigantic, malfunctioning system down into multiple complex circuits, you can figure out which circuit might be responsible for the problem. You can then split the complex circuit into simple ones and figure out which circuit is most likely the culprit. Within that rogue circuit, you can examine the components one at a time. If you follow such a process of elimination with the help of schematics, you can repair the equipment with less trouble than you’d go through if you didn’t have the diagrams. Whenever you go through this process, an engineer would say that you troubleshoot to the component level.
许多电子系统故障都是由单个元件的问题引起的。有时，这种故障还会导致其他元件也出现问题。偶尔你会发现两个或多个有缺陷的元件导致系统崩溃。单个问题。您必须熟悉系统，然后在学习并理解系统的正常运行状态后，利用原理图来大致了解未来可能出现故障的位置。每次发生故障时，按照此步骤操作，即可识别出最可疑的单个组件。然后，您只需在实际系统中找到这些组件，使用合适的测试仪器打开设备，逐一检查可疑组件即可。
Many electronic system failures arise from a problem with a single component. Sometimes this glitch will cause other components to go bad, too. Once in a while you’ll discover two or more defective components causing a single problem. You must familiarize yourself with the system, and then, after you’ve studied and understood the system’s normal operating state, you can use a schematic to get a good idea of where future troubles might arise. By following this procedure whenever malfunctions occur, you can identify the most suspect individual component(s). Then you need only find those component(s) in the physical system, get into the equipment with the appropriate test instrument, and check the suspect component(s) one by one.
熟悉大型原理图
Getting Comfortable with Large Schematics
无论你多么热爱电子产品，也不能指望初学者就能轻松阅读复杂的电路图。你需要循序渐进地学习。首先，你必须确保自己了解所有可能出现的电路符号。复杂的电路图可以作为很好的学习工具，因为它们包含大量的符号，其中一些你可能一开始并不认识。你可以利用这些电路图来帮助你学习这些符号。
No matter how much you enjoy electronics, you can’t expect to sit down as a beginner and read complicated schematics with ease. You need to climb a learning curve. First of all, you must make certain that you know every schematic symbol that you expect to see. Complex schematics can serve as a great learning tool, because they contain lots of symbols, some of which you probably won’t know at first. You can use these diagrams to help you learn the symbols.
一旦你熟悉了各种符号，就把复杂的电路图收起来，开始研究一些简单常见的电路图。你可以在电子爱好者的杂志上找到很多这样的电路图。（你也可以在麦格劳-希尔出版社出版的《在家就能做的电学实验》一书中找到许多简单的项目和相关的电路图。）不要将你的学习局限于一种类型的电路图，例如只研究放大器电路图。还要研究振荡器、电源、固态开关、射频电路、音频电路以及你能找到的任何其他电路。你会发现不同类型的电路之间存在相似之处，有时除了元件数值的细微差别外，几乎没有其他显著差异。当你能够通过电路图识别放大器、振荡器或检波器时，你就知道自己已经取得了进步。
Once you feel comfortable with the individual symbols, put away the complex schematics and start looking over diagrams of simple, common circuits. You’ll find lots of them in magazines for electronics enthusiasts. (You’ll also find plenty of simple projects and related diagrams in Electricity Experiments You Can Do at Home, published by McGraw-Hill.) Don’t limit your studies to one type of schematic, such as those that portray only amplifiers. Check into oscillators, power supplies, solid-state switches, RF circuits, AF circuits, and anything else you can find. You’ll discover similarities among different types of circuits, sometimes with no significant differences other than a few changes in component values. When you can identify an amplifier or oscillator or detector by looking at its schematic, then you’ll know that you’ve made progress.
下一步，你将学习一些结合了之前学过的简单电路的设备。有时你会看到一些额外的元件，它们能使一个电路的输出与另一个电路的输入在电气上匹配。选择一些既有理论讲解又有实践应用的书籍和出版物，这些书籍和出版物应涵盖电路原理图所示的电路。更好的办法是，在家里的工作室里搭建一些简单的电路。
Your next step will include devices that combine a few of the simple circuits you’ve previously studied. Sometimes you’ll see additional components that electrically match the output of one circuit to the input of another. Choose books and publications that offer both theoretical and practical discussions of the circuit that the schematic depicts. Even better, build some simple circuits in a home workshop.
当你看到自己亲手制作的第一个电子电路的实际样子与原理图相比时，你可能会感到惊讶。接下来，你需要继续学习，仔细观察电路的实际运行情况，并注意实际元件与原理图中元件之间的关系。你可以通过实验来扩展你的电子学知识（例如，替换不同的元件）。你或许能找到让电路运行得更好的方法。记录下你所做的改进，并绘制一张新的原理图来反映这些改进。如果你做的改动不多，可以直接在最初搭建电路的原理图上用铅笔标注这些改动。
You might get a surprise when you see how your first “homebrew” electronic circuit looks in real life when compared with the schematic. Your study will continue from this point by examining the functional circuit and noting the relationship of the physical components to those in the schematic. You can expand your electronics knowledge by experimenting with these circuits (substituting different components, for example). You might find a way to make the circuit work better than it originally did. Note the improvements that you make, and draw a new schematic that reflects them all. If you didn’t make many changes, you can pencil in the changes on the schematic from which you built the original circuit.
当你能够轻松地根据电路图搭建简单的电路时，你可能想要将两个或多个电路组合起来，制作一个更复杂的设备。从一本“项目”书中选取两张电路图，并将它们组合在纸上。你需要绘制自己的电路图，作为搭建步骤的指导。此时，你可能已经掌握了足够的知识，可以设计并搭建一个能够连接这两个电路的接口电路（将第一个电路的输出连接到第二个电路的输入，使它们都能发挥最佳性能）。将电路搭建与学习阅读和绘制电路图结合起来，比单纯地查看和绘制电路图更能有效地提升你的电子学知识。
When you feel comfortable building simple circuits from schematics, you might want to combine two or more circuits to make a more sophisticated device. Take two schematics from a “projects” book and combine them on paper. You’ll have to draw your own schematic to serve as a plan for the building procedure. You might know enough by this time to design and build a circuit that can interface the two (connect the output of the first circuit to the input of the second one so they both work at their best). When you combine circuit-building with the task of learning to read and create schematics, you’ll improve your electronics knowledge more easily than you can do by merely looking at, and drawing, the diagrams.
不知不觉中，你就会掌握扎实的电路图和电路搭建知识。那些你曾经觉得复杂的电路，现在看来都很简单。尽管如此，你仍应保持好奇心。你或许会倾向于只做自己最熟悉的电路，而不愿涉足新的领域。千万别让懒惰占据上风！一旦你感到得心应手，就应该挑战更复杂的电路图。不断搭建更复杂的项目。当然，过度练习也会增加成本，所以即使你无法搭建所有电路，也要坚持阅读电路图，理解各种电路元件。
Before you know it, you’ll have a solid knowledge of schematics and circuit-building. The circuits that you once imagined as complicated will seem elementary. Nevertheless, you should remain inquisitive. You might feel the temptation to stay with the types of circuits that you know best, and not venture into new territory. Don’t let laziness get the better of you! As soon as you reach one stage of comfort, move on to more difficult diagrams. Keep building more complex projects. Of course, this practice can grow expensive if you overdo it, so if you can’t build everything in sight, keep reading schematics and deciphering diverse circuit components anyway.
你永远都会对自己知道的和不知道的东西感到惊讶。例如，许多电子学新手认为商用调幅（AM）广播发射机一定是一个高度复杂的系统。但大多数电子学新手都会惊讶地发现，调幅发射机比你可能用来截获广播的老式晶体管袖珍接收机还要简单。商用广播发射机其实是一个相当简单的系统，即使它像你的汽车一样庞大。发射机的尺寸与元件的尺寸直接相关，而元件的尺寸又直接与系统消耗的功率相关。商用发射机的电源变压器本身就可能和你家的冰箱一样重！正是这些元件以及其他部件使得商用广播发射机体积庞大、重量沉重。而小型业余无线电发射机的电源变压器重量可能不到一公斤。尽管如此，在电路图中，这两个变压器看起来却是一样的。
You’ll forever stay amazed at what you know and what you don’t know. For instance, many electronics neophytes imagine that a commercial AM radio transmitter must be a highly complex system. Most electronics novices are astonished to learn that the AM transmitter is less complicated than an old-fashioned transistorized pocket receiver that you might use to intercept the broadcasts. A commercial radio transmitter is a rather simple system, even if it’s as big and massive as your car. The transmitter size directly correlates with the component size, which in turn directly relates to the amount of power that the system consumes. The power-supply transformer for a commercial transmitter, all by itself, might weigh as much as your home refrigerator! This and other components make the commercial broadcast transmitter large and heavy. The power-supply transformer for a small amateur radio transmitter will likely mass less than a kilogram. Nevertheless, both transformers will look the same in schematics.
体积最大的设备往往并非最复杂的，无论从电子结构还是电路图来看都是如此。那些可以握在手中的小型设备，如果拆解到元件层面，其电路图的复杂程度往往更胜一筹。平板电脑就是一个很好的例子。这类系统内部的集成电路（IC 或芯片）可能包含数百万个二极管、晶体管、电容器和电阻器。因此，电子学新手不应仅仅因为某个电路、设备或系统的尺寸看起来复杂就望而却步。你或许会判断错误，但即便你的判断正确，每张电路图也总会包含一些你可以理解的部分。
The most massive pieces of equipment are rarely the most complicated ones, both electronically and schematically. The tiny units that you can hold in the palm of your hand often take the prize for schematic complexity when you break them down to the component level. A tablet computer offers an excellent example. The integrated circuits (ICs or chips) inside such a system can contain millions of individual diodes, transistors, capacitors, and resistors. For this reason, an electronics novice should not shy away from any particular circuit, device, or system just because its size suggests complexity. You might be wrong, but even if you’re right, every schematic will contain portions that you can comprehend.
当你掌握了电路图的中级知识后，就可以着手处理复杂的电路、器件和系统了。你可以将它们分解成多个电路级或器件，最终简化成简单的电路。尝试获取那些能够完整详细解释电路工作原理的复杂电路图。
After you’ve gotten past the intermediate stage of learning schematics, then you can tackle complex circuits, devices, and systems. You can break them down into multiple-circuit stages or devices, and ultimately into simple circuits. Try to obtain schematics of a complex nature that offer a complete and detailed explanation of how the circuits work.
回想一下你在第二章中看到的图 2-2的频闪灯电路框图。将其与图 5-16进行比较，图 5-16 是一张显示所有独立元件的原理图。整个原理图是侧放的，以便整齐地显示在页面上。电路由 120 伏交流电供电，电源从原理图的左侧输入（旋转页面使原理图正向显示后）。交流电源线的三个端子分别沿着三条不同颜色的导线走线。黑色导线连接到保险丝，白色导线连接到电源和定时元件，绿色导线（来自插头的“第三个插脚”）连接到可靠的接地端。
Recall the block diagram of Fig. 2-2, the strobe light circuit that you saw in Chapter 2. Compare it to Fig. 5-16, a schematic that shows all the individual components. The whole diagram is tilted on its side, allowing it to fit on the page neatly. The circuit gets powered with 120 VAC, which enters at the left side of the schematic (after you rotate the page to make the diagram appear right-side up). The three terminals of the AC line take three separate paths along color-coded wires. A black wire goes to the fuse, a white wire goes to the power supply and timing components, and a green wire, coming from the “third prong” of the plug, goes to a substantial earth ground.
图 5-16为频闪灯电路的示意图，该电路最初在 图 2-2的框图中显示。为了将其放在一页上，整个图逆时针旋转了四分之一圈（90 度）。
FIG. 5-16 Schematic of the strobe light circuit originally shown in the block diagram of Fig. 2-2. In order to fit it on a single page, the entire diagram has been rotated counterclockwise by a quarter turn (90 degrees).
图 5-17A和5-17B显示与图 5-16相同的电路，只是将电路图分为两部分，以便所有元件都能正向排列。第一部分（图 5-17A）显示了电源和部分定时电路。第二部分（图 5-17B ）显示了频率调节电位器 R4 以及其余的定时电路、开关器件和为频闪灯提供所需电压的变压器。图 5-17A中三个向右的楔形元件直接连接到图 5-17B中对应的向左的楔形元件。
Figures 5-17A and B show the same circuit as Fig. 5-16 does, except that the diagram is split into two sections so that it can all go right-side-up. The first part (Fig. 5-17A) shows the power supply and some of the timing circuitry. The second part (Fig. 5-17B) shows the frequency-adjusting potentiometer R4 along with the rest of the timing circuitry, the switching device, and the transformer that provides the strobe light with the voltage that it needs. The three right-pointing wedges in Fig. 5-17A connect directly to their left-pointing counterparts in Fig. 5-17B.
图 5-17A 频闪灯电路的插头、保险丝和整流器部分。楔形 X、Y 和 Z 表示图 B 的延伸部分。
FIG. 5-17A The plug, fuse, and rectifier portions of the strobe light circuit. Wedges X, Y, and Z represent extensions to illustration B.
图 5-17B 频闪灯电路的定时和变压器部分。楔形 X、Y 和 Z 表示图 A 的延伸部分。
FIG. 5-17B The timing and transformer portions of the strobe light circuit. Wedges X, Y, and Z represent extensions from illustration A.
运算放大器电路
Op Amp Circuits
现在请回到第三章，重新阅读关于运算放大器的部分。读完之后，我们来看几个使用这些经典芯片的实际电路。所有这些电路都设计用于音频频段。
Now turn your attention back to Chapter 3 and re-read the section on op amps. After you’re finished, let’s take a look at a few real-world circuits that use these venerable little chips. All of these circuits are designed to work in the AF range.
图 5-18显示了一个用作同相宽带放大器的运算放大器。信号从同相输入端输入，负反馈流经反相输入端。如图所示，您可以在同相输入端和地之间添加一个电阻，以限制输入阻抗并提高放大器的稳定性。（如果输入阻抗由外部元件决定，或者您希望尽可能提高输入阻抗，则无需添加此电阻。）在任何同相宽带放大器中，输出波在很宽的频率范围内与输入波相位一致。您需要在反相输入端和地之间连接一个固定电阻，并在输出端和反相输入端之间连接另一个电阻，该电阻的阻值可以是固定的，也可以是可变的。
Figure 5-18 shows an op amp wired up as a non-inverting broadband amplifier. The signal comes into the non-inverting input while negative feedback flows through the inverting input. You can add a resistor between the non-inverting input and ground, as shown in this schematic, to limit the input impedance and provide some extra stability to the amplifier. (You need not include this resistor if external components determine the input impedance, or if you want to keep the input impedance as high as possible.) In any non-inverting broadband amplifier, the output wave emerges in phase coincidence with the input wave over a wide range of frequencies. You connect a fixed resistor between the inverting input and ground, and another resistor, which can have either fixed or variable value, between the output and the inverting input.
图 5-18 一种采用运算放大器的可变增益宽带音频放大器电路。该电路产生的输出信号与输入信号相位一致（“正向”）。
FIG. 5-18 A variable-gain, broadband AF amplifier circuit that uses an op amp. This circuit produces its output signal in phase coincidence (“right-side up”) with respect to the input signal.
图 5-19显示了一个用作反相宽带放大器的运算放大器。这种配置在许多与同相放大器相同的应用场景中都会用到。它类似于图 5-18的电路，区别在于输入信号连接到反相输入端而不是同相输入端。您可以在输入端和地之间添加一个电阻来限制输入信号。就像使用同相放大器一样，可以通过调节阻抗来增强稳定性。（如果输入阻抗由外部元件决定，或者您希望最大化输入阻抗，则无需使用此电阻。）在反相放大器中，输出波与输入波相位相反。您可以像图5-18所示电路那样，在输出端和反相输入端之间连接一个固定电阻或电位器。
Figure 5-19 shows an op amp serving as an inverting broadband amplifier. You’ll find this arrangement in many of the same scenarios as you see non-inverting amplifiers. It resembles the circuit of Fig. 5-18, except that the input signal goes to the inverting input rather than the non-inverting input. You can add a resistor between the input terminal and ground to limit the input impedance and enhance the stability, just as you can do with a non-inverting amplifier. (You won’t need this resistor if external components determine the input impedance, or if you want to maximize the input impedance.) In an inverting amplifier, the output wave emerges in phase opposition with respect to the input wave. You can connect either a fixed resistor or a potentiometer between the output and the inverting input, exactly as you would do with the circuit of Fig. 5-18.
图 5-19 另一个使用运算放大器的可变增益宽带音频放大器电路。该电路产生的输出信号与输入信号相位相反（“上下颠倒”）。
FIG. 5-19 Another variable-gain, broadband AF amplifier circuit using an op amp. This circuit produces its output signal in phase opposition (“upside down”) with respect to the input signal.
反相微分器是一种电路，其瞬时输出电平的变化与输入信号电平随时间变化的速率成反比。这种电路产生的输出信号与输入信号的频率相同，但波形可能（而且通常确实）不同。图5-20显示了一个用作反相微分器的运算放大器的原理图。该电路提供一定的增益。
An inverting differentiator is a circuit whose instantaneous output level varies in proportion to an upside-down version of the rate of change in the input signal level as a function of time. This arrangement produces an output signal with the same frequency as that of the input signal, although the waveform might (and often does) differ. Figure 5-20 shows a schematic of an op amp wired up as an inverting differentiator. This circuit provides some gain.
图 5-20 一个运算放大器电路，它可以反转和微分信号并提供一些增益。
FIG. 5-20 An op amp circuit that inverts and differentiates a signal and provides some gain.
反相积分器是一种电路，其瞬时输出电平随时间变化，并与累积输入信号电平的倒置形式成正比。输出信号的频率可能与输入信号相同，但不一定相同。（在某些情况下，输出与输入可能截然不同！）图 5-21显示了一个用作反相积分器的运算放大器的原理图。与图 5-20的电路一样，这种配置可以提供一定的增益。
An inverting integrator is a circuit whose instantaneous output level varies in proportion to an upside-down version of the accumulated input signal level as a function of time. The output signal might have the same frequency as the input signal, but not necessarily. (In some cases, the output differs drastically from the input!) Figure 5-21 shows a schematic of an op amp wired up as an inverting integrator. As with the circuit of Fig. 5-20, this arrangement provides some gain.
图 5-21 一个运算放大器电路，它可以反转和积分信号并提供一些增益。
FIG. 5-21 An op amp circuit that inverts and integrates a signal and provides some gain.
如果将特定组合的电阻器和电容器与运算放大器连接起来，就可以创建频率敏感的音频滤波器，这些滤波器还可以提供放大功能。工程师称它们为有源滤波器，因为它们需要有源信号。需要直流电（例如电池）才能工作。早在第三章，您就看到了四个增益与频率关系图，分别显示：
If you connect specialized groups of resistors and capacitors together with op amps, you can create frequency-sensitive AF filters that can also provide amplification. Engineers call them active filters because they need a source of DC electricity (such as a battery) in order to work. All the way back in Chapter 3, you saw four gain-versus-frequency graphs showing:
•有利于低频的低通响应（图 3-47A）。
• A lowpass response that favors low frequencies (Fig. 3-47A).
•有利于高频的高通响应（图 3-47B）。
• A highpass response that favors high frequencies (Fig. 3-47B).
•在单一频率下具有最大增益的共振峰（图 3-47C）。
• A resonant peak that has maximum gain at a single frequency (Fig. 3-47C).
•在单一频率下增益最小的谐振陷波（图 3-47D）。
• A resonant notch that has minimum gain at a single frequency (Fig. 3-47D).
图 5-22展示了如何连接运算放大器以产生低通响应。电阻 R 和电容 C 的值决定了截止频率（电压增益为 -3 dB 时的频率，约为最大增益的 70.7%）。截止频率会因以下情况而降低：
Figure 5-22 shows how you can wire up an op amp to produce a lowpass response. The values of resistor R and capacitor C determine the cutoff frequency (where the voltage gain is -3 dB, representing roughly 70.7 percent of maximum). The cutoff frequency drops if you:
图 5-22 一个运算放大器连接成低通滤波器。电阻R和电容C的值决定了截止频率。该电路提供一定的增益。
FIG. 5-22 An op amp wired up to serve as a lowpass filter. The values of resistor R and capacitor C determine the cutoff frequency. This circuit provides some gain.
• 增加电阻，但保持电容不变。
• Increase the resistance but leave the capacitance constant.
• 增加电容，但保持电阻不变。
• Increase the capacitance but leave the resistance constant.
• 同时增加电阻和电容。
• Increase both the resistance and the capacitance.
如果满足以下条件，截止频率会升高：
The cutoff frequency rises if you:
• 降低电阻，但保持电容不变。
• Decrease the resistance but leave the capacitance constant.
• 降低电容，但保持电阻不变。
• Decrease the capacitance but leave the resistance constant.
• 降低电阻和电容。
• Decrease both the resistance and the capacitance.
图 5-23是一个运算放大器、电阻 R 和电容 C 连接的电路图，用于产生高通响应。与低通滤波器类似，截止频率会随着以下情况而降低：
Figure 5-23 is a schematic of an op amp, a resistor R, and a capacitor C connected to produce a highpass response. As with the lowpass filter, the cutoff frequency drops if you:
图 5-23 一个运算放大器连接成高通滤波器。电阻R和电容C的值决定了截止频率。该电路提供一定的增益。
FIG. 5-23 An op amp wired up to serve as a highpass filter. The values of resistor R and capacitor C determine the cutoff frequency. This circuit provides some gain.
• 增加电阻，但保持电容不变。
• Increase the resistance but leave the capacitance constant.
• 增加电容，但保持电阻不变。
• Increase the capacitance but leave the resistance constant.
• 同时增加电阻和电容。
• Increase both the resistance and the capacitance.
如果满足以下条件，截止频率会升高：
The cutoff frequency rises if you:
• 降低电阻，但保持电容不变。
• Decrease the resistance but leave the capacitance constant.
• 降低电容，但保持电阻不变。
• Decrease the capacitance but leave the resistance constant.
• 降低电阻和电容。
• Decrease both the resistance and the capacitance.
为了计算图 5-22所示低通滤波器或图 5-23所示高通滤波器的截止频率f（单位：赫兹），您需要知道电阻R（单位：欧姆）和电容C（单位：法拉）。然后您可以使用以下公式。
In order to calculate the cutoff frequency f (in hertz) of the lowpass filter of Fig. 5-22 or the highpass filter of Fig. 5-23, you need to know the resistance R in ohms and the capacitance C in farads. Then you can use the formula
f = 1 / (2π RC )
f = 1 / (2πRC)
其中 π 代表圆的周长与其直径之比（约等于 3.14159）。即使电阻R的单位是兆欧，电容C 的单位是微法，这个公式仍然适用。（频率f 的单位仍然是赫兹。）
where π represents the ratio of a circle’s circumference to its diameter (approximately 3.14159). This formula will also work if you express R in megohms and C in microfarads. (The frequency f will still come out in hertz.)
图 5-24是一个运算放大器、两个电阻 R1 和 R2 以及两个电容 C1 和 C2 的电路原理图，它们连接在一起以产生谐振峰值响应。如果发生以下情况，谐振峰值（最大增益）频率会下降：
Figure 5-24 is a schematic of an op amp, two resistors R1 and R2, and two capacitors C1 and C2 connected to produce a resonant peak response. The resonant peak (maximum gain) frequency drops if you:
图 5-24 一个运算放大器连接成谐振峰值滤波器。电阻器R1 、 R2 、电容器 C1和C2的值决定了谐振频率。
FIG. 5-24 An op amp wired up to serve as a resonant peak filter. The values of resistors and capacitors R1, R2, C1, and C2 determine the resonant frequency.
• 增加电阻，但保持电容不变。
• Increase the resistances but leave the capacitances constant.
• 增加电容，但保持电阻不变。
• Increase the capacitances but leave the resistances constant.
• 增加电阻和电容。
• Increase both resistances and both capacitances.
如果满足以下条件，共振峰值频率会升高：
The resonant peak frequency rises if you:
• 降低电阻，但保持电容不变。
• Decrease the resistances but leave the capacitances constant.
• 降低电容，但保持电阻不变。
• Decrease the capacitances but leave the resistances constant.
• 降低电阻和电容。
• Decrease both resistances and both capacitances.
要计算谐振峰值频率f（单位为赫兹），您需要知道电阻值R₁和R₂ （单位为欧姆）以及电容值C₁和C₂（单位为法拉）。然后您可以使用以下公式。
To calculate the resonant peak frequency f (in hertz), you need to know the resistance values R1 and R2 in ohms and the capacitance values C1 and C2 in farads. Then you can use the formula
f = 1 / [ 2π ( R 1 R 2 C 1 C 2) 1/2 ]
f = 1 / [ 2π (R1 R2 C1 C2)1/2 ]
如果将电阻值都用兆欧表示，电容值都用微法表示，那么这个公式也可以得出以赫兹为单位的f 值。
This formula will also yield f in hertz if you express both resistances in megohms and both capacitances in microfarads.
图 5-25是一个运算放大器、四个电阻 R1 至 R4 和两个电容 C1 和 C2 的电路图，它们连接在一起以产生谐振陷波响应。在该电路中，电阻R1和R2分别控制陷波频率以上和以下的增益。电阻R3和R4应相等；我们称该电阻为R。此外，电容C1和C2也应相等；我们称该电容为C。
Figure 5-25 is a schematic of an op amp, four resistors R1 through R4, and two capacitors C1 and C2 connected to produce a resonant notch response. In this circuit, resistances R1 and R2 govern the gain at frequencies above and below that of the notch. Resistances R3 and R4 should equal each other; let’s call that resistance R. In addition, capacitances C1 and C2 should equal each other; let’s call that capacitance C.
图 5-25 一个运算放大器连接成谐振陷波滤波器。电阻和电容的值决定了谐振频率。在这个电路中，R3 = R4；你可以称这个电阻为 R。此外，C1 = C2；你可以称这个电容为 C。
FIG. 5-25 An op amp wired up to serve as a resonant notch filter. The values of resistors and capacitors determine the resonant frequency. In this circuit, R3 = R4; you can call this resistance R. Also, C1 = C2; you can call this capacitance C.
如果执行以下操作，谐振陷波（或最小增益）频率会下降：
The resonant notch (or minimum gain) frequency drops if you:
• 增加R，但保持C不变。
• Increase R but leave C constant.
• 增加C，但保持R不变。
• Increase C but leave R constant.
•增加R和C。
• Increase both R and C.
如果满足以下条件，共振陷波频率会升高：
The resonant notch frequency rises if you:
• 降低R 值，但保持C值不变。
• Decrease R but leave C constant.
• 降低C但保持R不变。
• Decrease C but leave R constant.
•降低R和C。
• Decrease both R and C.
要计算谐振陷波频率f（单位为赫兹），您需要知道R和C 的值，如上定义，单位分别为欧姆和法拉。然后您可以使用以下公式。
To calculate the resonant notch frequency f (in hertz), you need to know R and C, as defined above, in ohms and farads respectively. Then you can use the formula
f = 1 / (2π RC )
f = 1 / (2πRC)
如果将R 3 和R 4 都以兆欧为单位表示，将C 3 和C 4 都以微法为单位表示，则该公式还可以得出以赫兹为单位的 f 。
This formula will also yield f in hertz if you express both R3 and R4 in megohms and both C3 and C4 in microfarads.
概括
Summary
阅读和绘制电路图通常需要将复杂的电路分解成简单的电路。这样你就可以观察系统的各个部分以及它们之间的关系，而不是试图将整个系统想象成一个单一的设备。当你研究复杂的电路图时，电路之间的关系会逐渐清晰。有时，你会突然发现系统的所有“秘密”都揭晓了：恍然大悟的时刻！
Reading and drawing schematics often involve breaking down complex circuits into simple ones. Then you can look at the system’s parts and how they relate to each other, rather than try to imagine the whole thing as a single appliance. As you study a complex schematic, the relationships among the circuits will grow apparent. Once in awhile, you’ll see all of a system’s “secrets” revealed at once: an “Aha” moment!
学习读写电路图与学习收发古老的摩尔斯电码非常相似。“电码”是一种由可听见的符号组成的语言，正如电路图是一种由印刷符号组成的语言。一旦掌握了其中任何一种语言，你都可以用它来交流；摩尔斯电码用于传递单词和句子，而电路图用于传达原理和概念。
Learning to read and write schematics is a lot like learning to receive and send the old Morse code. “The code” is a language of audible symbols, just like a schematic is a language of printed symbols. Once you learn either language, you can use it to communicate; Morse code communicates words and sentences, while schematics communicate principles and concepts.
以摩尔斯电码为例，一长串点和划线如果没有被分解成单词，就毫无意义。随着熟练程度的提高，你将不再听到单个的点和划线（或者像有些人说的“滴”和“嗒”），而是听到字母。继续练习，你就能听到完整的单词。最终，如果你坚持足够长的时间（尤其是如果你像我多年来作为业余无线电爱好者那样，对摩尔斯电码本身产生了兴趣，并连续几个小时用它进行交流），你就能听到完整的短语和句子。
Using Morse code as a further example, a long sequence of dots and dashes will mean nothing unless you can break the data down into words. As your proficiency increases, you’ll stop hearing the individual dots and dashes (or, as some people say, “dits” and “dahs”) and hear letters of the alphabet instead. As you keep practicing, you’ll start to hear entire words. Eventually, if you keep at it long enough (and especially if you get fond of the code for its own sake, communicating with it for hours on end, as I have done over the years as a ham radio operator), you’ll hear whole phrases and sentences.
阅读和绘制电路图的过程与学习电路图的学习过程类似。起初，你会看到单个元件的符号。之后，你会发现隐藏在复杂电路中的简单电路。接着，你会识别并分析这些复杂电路。最终，你将能够构想出完整的系统。这些知识的积累或许需要时间，但只要你不断（当然要循序渐进地）探索新的知识领域，你的熟练程度就会随着练习而提高。
Reading and writing schematics takes you through a similar pattern of development. At first you’ll see individual component symbols. Later, you’ll find simple circuits hidden within complex circuits. Then you’ll identify and analyze those complex circuits. Finally, you’ll envision entire systems. This knowledge might come slowly, but your proficiency will improve every time you practice if you keep pushing yourself (gently, of course) into new knowledge zones.
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用于构建和测试的图表
Diagrams for Building and Testing
几年前，麦格劳-希尔出版社出版了我的著作《在家就能做的电学实验》。本章收录了书中的一些实验，并附有图示和示意图。这些实验可以帮助您熟练地阅读和理解电路图、示意图以及实际电路。我们先从一些设置细节开始，包括零件清单和面包板的搭建。如果您感兴趣，可以尝试这些实验。如果您喜欢这些实验，可以购买《在家就能做的电学实验》一书，进行更多实验！
Several years ago, McGraw-Hill published my book Electricity Experiments You Can Do at Home. This chapter contains a few experiments from that book along with drawings and diagrams. These experiments can help you gain proficiency in reading and interpreting schematics, pictorials, and real-world circuits. Let’s start with some setup details including a parts list and the construction of a circuit board called a breadboard. Then you can try these experiments if you like. If you enjoy them, you can get a copy of Electricity Experiments You Can Do at Home and do more!
你的面包板
Your Breadboard
每个实验者都需要一个好的工作台。我的工作台是用一块胶合板做成的，上面压着一块旧立式钢琴的键盘，再用镀黄铜的链条挂在地下室的天花板上。你的工作台不必这么奇特，只要不晃动或坍塌，放在任何地方都行。工作台面最好用坚固的非导电材料，比如木头，上面铺一层塑料垫或一小块短绒地毯（门垫就很好用）。再配上一盏台灯，最好是那种带可调节灯臂的“高强度”台灯，就大功告成了。
Every experimenter needs a good workbench. Mine comprises a piece of plywood, weighted down over the keyboard of an old upright piano, and hung from the cellar ceiling by brass-plated chains. Yours doesn’t have to be that exotic. You can put it anywhere as long as it won’t shake or collapse. You should make the surface out of a solid non-conducting material such as wood, protected by a plastic mat or a small piece of close-cropped carpet (a doormat works great). A desk lamp, preferably the “high-intensity” type with an adjustable arm, completes the ensemble.
在开始本章所述的任何任务之前，请先到当地的五金店购买一副安全眼镜。在搭建和测试这些电路时，务必佩戴眼镜。养成佩戴安全眼镜的习惯，无论你是否认为需要。你永远无法预料，当你用斜口钳剪断电线时，一小段电线会不会飞向你的眼睛！
Before you begin any of the tasks described in this chapter, buy a pair of safety glasses at your local hardware store. Wear the glasses whenever you build and test these circuits. Get into the habit of wearing safety glasses whether you think you need them or not. You never know when a little piece of wire will fly at one of your eyes as you snip it off with diagonal cutter!
表 6-1 电力实验所需元件清单。您可以在零售商店找到这些元件，也可以从本书附录C
中列出的供应商处订购。缩写：AWG = 美国线规，A = 安培，V = 伏特，W = 瓦特，PIV = 峰值反向电压。在某些情况下，此表包含的元件可能比您需要的要多。
（您永远不知道什么时候会需要一两个“备用”元件！）
TABLE 6-1 Components list for electricity experiments. You can find these items at retail stores or order them from vendors such as those in Appendix C at the back of this book.
Abbreviations: AWG = American Wire Gauge, A = amperes, V = volts, W = watts, and PIV = peak inverse volts. In some cases this table includes more items than you’ll likely need.
(You never know when you’ll want an “extra” or two!)
你的面包板不必看起来很精致，也不必很贵。我去当地一家木材厂买了木材。我在他们的废料堆里找到了一块“12英寸×3/4英寸”的松木。一块“12英寸”的木板实际宽度约为10.8英寸（27.4厘米），实际厚度约为0.6英寸（15毫米）。木材厂的人没收我木材本身的费用，但他们收了我几美元的切割费，帮我把木板切割成一块12.5英寸（31.8厘米）长的长方形松木。
Your breadboard doesn’t have to look fancy or cost much money. I patronized a local lumber yard to get the wood for mine. I found a length of “12-inch by 3/4-inch” pine in their scrap heap. The actual width of a “12-inch” board is about 10.8 inches (27.4 centimeters), and the actual thickness is about 0.6 inch (15 millimeters). The people at the lumber yard didn’t charge me anything for the wood itself, but they demanded a couple of dollars to make a clean cut to produce a rectangular piece of pine measuring 12.5 inches (31.8 centimeters) long.
用尺子将面包板沿长度方向以 1 英寸（25.4 毫米）为间隔进行分界，中心点处共分出 11 个等距的标记。沿横向方向重复此操作，得到 9 个以 1 英寸（25.4 毫米）为间隔的标记。用圆珠笔或走珠笔在面包板边缘画出平行线，形成网格。将网格线分别标记为 A 到 K 和 0 到 9。如图 6-1所示。这样就能得到 99 个交点，每个交点都可以用字母/数字对来表示，例如 D-3 或 G-8。
Using a ruler, divide the breadboard lengthwise at 1-inch (25.4-millimeter) intervals, centered to get 11 evenly spaced marks. Do the same thing going sideways to obtain nine marks at 1-inch (25.4-millimeter) intervals. Using a ball-point or roller-point pen, draw lines parallel to the edges of the board to make a grid pattern. Label the grid lines from A to K and 0 to 9 as shown in Fig. 6-1. That’ll give you 99 intersection points, each of which you can designate with a letter/number pair such as D-3 or G-8.
图 6-1 电学实验的面包板布局。实心点表示钉子位置。网格正方形尺寸为 1 英寸 x 1 英寸（25.4 毫米 x 25.4 毫米）。
FIG. 6-1 Breadboard layout for electricity experiments. Solid dots show nail locations. Grid squares measure 1 by 1 inch (25.4 by 25.4 millimeters).
画好网格线后，准备一些 1.25 英寸（31.8 毫米）的抛光钢钉。将木板放在坚固的表面上，确保表面不会被刮擦损坏。如图 6-1中黑点所示，在每个交点处钉入一颗钉子。务必确保钉子头部很小，并且没有涂漆、塑料、清漆或其他绝缘材料。每颗钉子钉入木板的深度应刚好足以固定住，不会晃动。我将每颗钉子钉入约 0.3 英寸（8 毫米）深，大约是木板厚度的一半。
Once you’ve marked the grid lines, gather together a bunch of 1.25-inch (31.8-millimeter) polished steel finishing nails. Place the board on a solid surface that can’t suffer any damage from scratching or scraping. Pound a nail into each intersection point shown by the black dots in Fig. 6-1. Make certain that the nails have “tiny heads” and do not have any coating of paint, plastic, lacquer, or other electrically insulating material. Each nail should go into the board just far enough so that you can’t wiggle it around. I pounded every nail down to a depth of approximately 0.3 inch (8 millimeters), a distance amounting to halfway through the board.
使用 6 × 32 平头木螺钉将两个微型灯座固定到图 6-1所示的位置。用短段细实心裸铜线将其中一个灯座的接线端子连接到面包板钉 A-2 和 D-1。将另一个灯座的接线端子连接到钉子 D-2 和 G-1。将铜线紧紧地缠绕在每个钉子上三到四圈。剪掉多余的铜线。用接触胶将四节 AA 电池座粘到面包板上。等待胶水固化。这个过程需要几个小时，所以你可以休息一会儿！
Use some 6 × 32 flat-head wood screws to secure the two miniature lamp holders to the board at the locations shown in Fig. 6-1. Connect the terminals of one lamp holder to breadboard nails A-2 and D-1 with short lengths of thin, solid, bare copper wire. Connect the terminals of the other lamp holder to nails D-2 and G-1. Wrap the wire tightly three or four times around each nail. Snip off any excess wire that remains. Glue the four-cell AA battery holder to the breadboard with contact cement. Allow the cement to harden. That process will need a few hours, so you can take a break for awhile!
待接触胶凝固后，剥去电池座引线末端约 25.4 毫米（1 英寸）的绝缘层，并将引线如图6-1所示连接到钉子上。请记住，红色引线连接到电池正极，黑色引线连接到负极。使用与灯座引线相同的绕线方法。将四节全新的 AA 碱性电池放入电池座中。将负极接在弹簧上。我建议你买一包四节电池，这样它们的状态都一样“新鲜”。现在你就有了一个 6V 的电池组，面包板就等着你大显身手了。
When the contact cement has solidified, strip approximately 1 inch (25.4 millimeters) of the insulation from the ends of the cell-holder leads and connect the leads to the nails as shown in Fig. 6-1. Remember that the red lead goes to the positive battery terminal, and the black lead goes to the negative terminal. Use the same wire-wrapping technique that you did for the lamp-holder wires. Place four brand new AA alkaline cells in the holders with the negative terminals against the springs. I recommend that you buy a single package of four cells so that they’re all equally “fresh.” Now you have a 6-V battery, and the breadboard awaits your exploits.
绕线
Wire Wrapping
以下基于面包板的实验采用了一种称为绕线法的搭建方法。每个钉子都形成一个接线端子，您可以将元件引脚或导线连接到该端子上。要进行连接，请将裸露的导线或引脚紧紧地缠绕在钉子上。如图 6-2所示，缠绕四到五圈即可。
The following breadboard-based experiments employ a construction method called wire wrapping. Each nail forms a terminal to which you can attach component leads or wires. To make a connection, tightly wrap an uninsulated wire or lead around a nail. Make four or five complete wire turns as shown in Fig. 6-2.
图 6-2 绕线法。如有必要，可以使用斜口钳剪掉多余的线。
FIG. 6-2 Wire-wrapping technique. If necessary, you can use a diagonal cutter to snip off excess wire.
将一段导线末端缠绕好后，剪掉多余的部分。对于电阻器和二极管等小型元件，将引脚缠绕在钉子上，直到用完所有引脚长度。这样，就无需剪断元件引脚，而且之后还可以解开缠绕，将这些元件用于其他实验。尖嘴钳可以帮助您缠绕手指无法缠绕的导线或引脚。
After you wrap the end of a length of wire, cut off the excess. For small components such as resistors and diodes, wrap the leads around the nails as many times as it takes to use up the entire lead length. That way, you won’t have to cut down the component leads, and you can later unwrap and reuse the components for other experiments. Needle-nose pliers can help you to wrap wires or leads that you can’t wrap with your fingers alone.
当你想把多根电线连接到同一根钉子上时，你可以把一根电线或导线缠绕在另一根电线或导线上，但除非钉子空间不够，否则你不需要这样做。每根钉子都应该突出板面足够高，这样你就不会经常遇到缠绕空间不足的情况。
When you want to make multiple connections to a single nail, you can wrap one wire or lead over the other, but you shouldn’t have to do that unless you’ve run out of nail space. Each nail should protrude far enough above the board surface so that you won’t get cramped for wrapping space very often.
在搭建后续电路时，您可以根据需要调整面包板上元件的布局。我提供了原理图和图示，向您展示元件之间的连接方式。我建议您遵循我的布局建议。这样，即使您没有实际搭建面包板并操作硬件，也可以专注于比较电路的实际外观与原理图。
As you build the circuits that follow, you can tailor the arrangement of parts on the breadboard to suit your needs. I’ve provided schematic and pictorial diagrams to show you how the components interconnect. I recommend that you follow my layout suggestions. That way, you can focus on how the actual appearance of the circuit compares with the schematic, even if you haven’t bothered to build the breadboard and work with the hardware directly.
电阻器等小型元件应放置在相邻的钉子之间（直线或斜线均可），以便将每根引脚牢固地缠绕在钉子上。如果钉子之间的距离过远，元件引脚可能不够长，无法进行有效的缠绕。您应该将跳线（也称为鳄鱼夹）固定在钉子上，以防止其“夹口”轻易松脱。我建议您将跳线横向夹在钉子上，使导线水平伸出。如果您尝试将这种所谓的鳄鱼夹垂直夹在钉子上，它可能会在您执行关键任务时突然脱落！
Small components such as resistors should go between adjacent nails (either straight or diagonally) so you can wrap each lead securely around each nail. If the nails lie too distant from each other, the component leads might not reach far enough to allow decent wrappings. You should secure jumper wires, also known as clip leads, to the nails so that their “jaws” can’t easily work their way loose. I suggest that you clamp the jumpers to the nails sideways so the wires come off horizontally. If you try to put one of these so-called alligator clips down on a nail vertically, it might pop off in the middle of a mission-critical operation!
基尔霍夫电流定律
Kirchhoff’s Current Law
在这个实验中，你将搭建一个电路，演示直流电中最重要的原理之一。你需要五个电阻：两个阻值为 330 欧姆，一个阻值为 1000 欧姆（1 千欧），两个阻值为 1500 欧姆（1.5 千欧）。你还需要四节 AA 电池。在我看来，金霸王 (Duracell) 和劲量 (Eveready) 在美国销售的电化学电池是最好的。
In this experiment, you’ll construct a network that demonstrates one of the most important principles in DC electricity. You’ll need five resistors: two rated at 330 ohms, one rated at 1000 ohms (1 k), and two rated at 1500 ohms (1.5 k). You’ll also need four AA cells. In my opinion, Duracell and Eveready sell the best electrochemical cells and batteries in the United States.
如图 6-3所示，将电阻器连接到面包板上的各对端子之间，并安装到位。安装前，请使用万用表（设置为欧姆表模式）测试每个电阻器的阻值。使用 13 厘米（5 英寸）长的裸铜线连接端子 I-1、J-1 和 K-1。对端子 I-3、J-3 和 K-3 以及 I-5、J-5 和 K-5 也进行同样的连接。
Mount the resistors on the breadboard by connecting them between pairs of terminals as shown in Fig. 6-3. Test each resistor with your multimeter (set to function as an ohmmeter) to verify its ohmic value before you install it. Use a 5-inch (13-centimeter) length of bare copper wire to interconnect the three terminals I-1, J-1, and K-1. Do the same thing with I-3, J-3, and K-3, and also with I-5, J-5, and K-5.
图 6-3 用于演示基尔霍夫电流定律的面包板上电阻器排列示意图。所有电阻值均以欧姆为单位。实心圆点表示面包板端子。实线表示与裸铜线的连接。虚线表示跳线。
FIG. 6-3 Arrangement of resistors on breadboard for demonstration of Kirchhoff’s current law. All resistance values are in ohms. Solid dots indicate breadboard terminals. Solid lines show interconnections with bare copper wire. Dashed lines indicate jumpers.
古斯塔夫·罗伯特·基尔霍夫（1824-1887）在人们对电流知之甚少的时代进行了研究并提出了理论。他运用常识推导出了直流电路的基本特性。基尔霍夫认为，流入电路中任何分支点的电流都等于直流电路中任何分支点的电流。必须始终等于流出该点的电流。无论有多少分支电流流入某一点，也无论有多少分支电流流出该点，基尔霍夫电流定律都成立。
Gustav Robert Kirchhoff (1824–1887) did research and formulated theories in a time when people didn’t know much about electrical current. He used common sense to deduce the fundamental properties of DC circuits. Kirchhoff reasoned that the current entering any branch point in a circuit must always equal the current leaving that point. Kirchhoff’s current law holds true no matter how many branches enter a given point, and no matter how many branches leave it.
图 6-4 根据基尔霍夫电流定律，流入任何支路点的电流之和始终等于流出该支路点的电流之和。在本例中，I1 + I2 = I3 + I4 + I5。
FIG. 6-4 According to Kirchhoff’s current law, the sum of the currents flowing into any branch point always equals the sum of the currents flowing out of that branch point. In this example, I1 + I2 = I3 + I4 + I5.
将四节电池连接到电阻网络，并测量每个支路中的电流。在所有其他测试点用跳线短接的情况下，分别测量每个测试点。图 6-5的原理图显示了我的网络中电阻的实际值（你的电阻值无疑会与我的略有不同），以及我测量 I₁ 时得到的值，即流过两个输入电阻中较小电阻的电流。
Connect your four-cell battery to the resistive network and measure the currents in each branch. Meter each test point individually while all the other test points remain shorted with jumpers. The schematic of Figure 6-5 shows the actual values of the resistors in my network (yours will doubtless differ slightly from mine), along with the value I got when I measured I1, the current through the smaller of the two input resistors.
图 6-5 用于验证基尔霍夫电流定律的网络。所有电阻值均以欧姆为单位。电池电压、电流 I₁和电阻值均为我的测量值。虚线表示用跳线连接的电路。
FIG. 6-5 Network for verifying Kirchhoff’s current law. All resistance values are in ohms. The battery voltage, the current I1, and the resistances indicate my measurements. Dashed lines show interconnections with jumpers.
测量每个电流值时，请确保仪表的极性与电池的极性一致。黑色探针应连接到负极，红色探针应连接到正极。这样可以避免出现负电流读数，从而影响您的计算结果。当我测试四节电池的电压时，得到 6.32 V。当我测量电流I1至I5时，得到以下结果，精确到毫安 (mA) 的百分之一：
As you measure each current value, make sure that the meter polarity agrees with the battery polarity. The black probe should go to the more negative point, and the red probe should go to the more positive point. That way, you’ll avoid negative current readings that might throw off your calculations. When I tested my four-cell battery to determine its voltage, I got 6.32 V. When I measured I1 through I5, I got the following results, accurate to the nearest hundredth of a milliampere (mA):
I₁ = 10.59 mA
I1 = 10.59 mA
I₂ = 2.40 mA
I2 = 2.40 mA
I₃ = 8.35 mA
I3 = 8.35 mA
I 4 = 2.79 mA
I4 = 2.79 mA
I 5 = 1.88 mA
I5 = 1.88 mA
再次强调，务必确保所有未进行电流测量的测试点对都用跳线短接。否则，网络将不完整，电流测量结果将不准确。测量完成后，移除所有跳线以节省电池电量。
Again, make certain that every pair of test points not undergoing current measurement gets shorted together with jumpers. Otherwise, you’ll have an incomplete network, and your current measurements will turn out wrong. After you’ve finished making the measurements, remove all the jumpers to conserve battery energy.
现在您可以将数值代入基尔霍夫公式，看看输入电流之和与输出电流之和有多接近。以下是我计算出的支路入口电流之和的结果：
Now you can input your numbers to the Kirchhoff formulas and see how close the sum of the input currents comes to the sum of the output currents. Here are my results for the sum of the currents entering the branch point:
当我把离开分支点的电流加起来时，我得到了
When I added the currents leaving the branch point, I got
基尔霍夫电压定律
Kirchhoff’s Voltage Law
在这个实验中，你将搭建一个电路来演示直流电路的另一个重要规律。你需要四个电阻：一个额定阻值为 220 欧姆，一个额定阻值为 330 欧姆，一个额定阻值为 470 欧姆，一个额定阻值为 680 欧姆。你还需要四节 AA 电池。
In this experiment, you’ll construct a network that demonstrates another important DC circuit rule. You’ll need four resistors: one rated at 220 ohms, one rated at 330 ohms, one rated at 470 ohms, and one rated at 680 ohms. You’ll need four AA cells again, too.
根据基尔霍夫电压定律，串联直流电路中各元件两端的电势（电压）之和（考虑极性）始终等于零。这条定律也可以称为基尔霍夫第二定律或电压守恒原理。
According to Kirchhoff’s voltage law, the sum of the potentials (voltages) across the individual components in a series DC circuit, taking polarity into account, always equals zero. You can also call this rule Kirchhoff’s second law or the principle of voltage conservation.
思考各种可能性
Ponder the Potentials
图 6-6展示了基尔霍夫电压定律的一个通用示例。电池电势E等于各电阻两端电势之和。每个电阻两端的极性与电池的极性相反，因此：
Figure 6-6 shows a generic example of Kirchhoff’s voltage law. The battery potential, E, equals the sum of the potentials across the resistors. The polarity across each resistor opposes the polarity of the battery, so that:
图 6-6 根据基尔霍夫电压定律，串联直流电路中各电阻两端的电压之和始终等于电池电压，但极性相反。如果忽略极性，则在本例中将得到 E = E 1 + E 2 + E 3 + E 4。
FIG. 6-6 According to Kirchhoff’s voltage law, the sum of the voltages across the resistances in a series DC circuit always equals the battery voltage, but with the opposite polarity. If you disregard polarity, then in this example you’ll get E = E1 + E2 + E3 + E4.
E + E1 + E2 + E3 + E4 = 0
E + E1 + E2 + E3 + E4 = 0
如果用直流电压表逐一测量各个电阻器和电池两端的电位，并且忽略极性，你会发现：
If you measure the potentials across the individual resistors and the battery, one at a time, with a DC voltmeter and disregard the polarity, you’ll find that:
E = E1 + E2 + E3 + E4
E = E1 + E2 + E3 + E4
在将四个电阻器安装到电路之前，请用欧姆表分别测量它们的阻值。将电阻器安装在面包板右上角，方法是将电阻器的引脚缠绕在钉子上，如图 6-7所示。按照指示用跳线将电池连接到电路，然后测量每个电阻器两端的电压。图 6-8显示了我的电路中电阻器的实际阻值（你的电路中的电阻器阻值可能略有不同），以及E2出现的电阻器。我将电池连接到电阻器时，测得电池两端的电压为 E = 6.30 V。
Check each of the four resistors with your ohmmeter to verify their values before you install them in the circuit. Mount the resistors in the upper right-hand corner of your breadboard by wrapping the leads around the nails to get the arrangement of Fig. 6-7. Connect the battery to the network with jumpers as indicated, and then measure the voltage across each resistor. Figure 6-8 illustrates the actual values of the resistors in my network (no doubt yours will differ a bit), along with the resistance across which E2 appeared. I measured E = 6.30 V across the battery when I connected it to the resistors.
图 6-7 面包板上电阻器的排列方式示意图，用于演示基尔霍夫电压定律。所有电阻值均以欧姆为单位。实心点表示端子。虚线表示跳线。
FIG. 6-7 Suggested arrangement of resistors on breadboard for demonstration of Kirchhoff’s voltage law. All resistance values are in ohms. Solid dots indicate terminals. Dashed lines indicate jumpers.
图 6-8 用于验证基尔霍夫电压定律的网络。所有电阻的单位均为欧姆。电池电压 E、第二个电阻两端的电压以及电阻值均为我测量所得。
FIG. 6-8 Network for verifying Kirchhoff’s voltage law. All resistances are in ohms. The battery voltage E, the voltage across the second resistor, and the resistances are the values I measured.
测量电压E1至E4时，黑色表笔应接在电压较低的点，红色表笔应接在电压较高的点，以避免出现可能影响计算结果的负值读数。当我测量各个电阻两端的电压时，我得到了……
As you measure each voltage E1 through E4, the black meter probe should go to the more negative voltage point and the red probe should go to the more positive point to avoid negative readings that could mess up your calculations. When I measured the voltages across the individual resistors, I got
测量完成后，拆掉一根跳线，以减轻电池的压力。
When you finish making your measurements, remove one of the jumpers to take the stress off the battery.
仔细核对并记录电压测量结果后，将这些数值代入修正后的基尔霍夫公式：
After you’ve double-checked and written down your voltage measurements, input the numbers to the modified Kirchhoff formula:
E = E1 + E2 + E3 + E4
E = E1 + E2 + E3 + E4
看看结果有多接近。我得到了以下结果：
and see how closely it works out. I got the following results:
E = 6.30 V
E = 6.30 V
和：
and:
在总电压为 6.30 V 的情况下，误差仅为 0.01 V，不到百分之二。
That’s an error of only 0.01 V out of a total potential of 6.30 V, amounting to less than two-tenths of one percent.
电阻分压器
A Resistive Voltage Divider
你可以使用之前实验中的元件，从单个电池中获得几种不同的电压。电阻器仍然留在面包板上。按照你在基尔霍夫电压定律实验中的排列方式进行排列。
You can use the components from the previous experiment to get several different voltages from a single battery. Keep the resistors on the breadboard in the same arrangement as you had them in the experiment for Kirchhoff’s voltage law.
当两个或多个电阻串联连接到直流电源时，这些电阻会产生不同的电压比。您可以使用特定的电阻来“固定”中间电压，从而调整这些电压比。当电路中串联电阻的阻值远小于任何外部负载的阻值时，电路工作效果最佳。
When you connect two or more resistors in series with a DC power source, those resistors produce various voltage ratios. You can tailor these ratios using specific resistances that “fix” the intermediate voltages. The circuit works best when your network resistors have values much smaller than the resistance of any external load that you place across the combination.
图 6-9展示了电阻分压器的原理。各个电阻分别为R1 、R2、R3 、 …和Rn 。总电阻R等于它们之和：
Figure 6-9 illustrates the principle of a resistive voltage divider. The individual resistances are R1, R2, R3, …, and Rn. The total resistance R equals their sum:
图 6-9 电压分压器利用与直流电源串联的各个电阻器两端的电位差。请注意，电压、测试点和电阻值均以斜体字标出。
FIG. 6-9 A voltage divider takes advantage of the potential differences across individual resistors connected in series with a DC power source. Note the use of italics for voltages, test points, and resistances.
R = R 1 + R 2 + R 3 + … + R n
R = R1 + R2 + R3 + … + Rn
在P1 、P2 、P3 、 …、Pn点，我们分别将相对于电池负极的电压记为E1 、E2 、 E3 、…、En。最后一个（也是最高）电压 En等于电池电压E。各点的电压根据到达该点的电阻总和的倍数递增，该倍数与总电阻乘以电池电压成正比。理论上，以下等式成立：
At points P1, P2, P3, …, and Pn, let’s call the voltages relative to the negative battery terminal E1, E2, E3, …, and En, respectively. The last (and highest) voltage, En, equals the battery voltage, E. The voltages at the various points increase according to the sum total of the resistances up to each point, in proportion to the total resistance, multiplied by the battery voltage. In theory, the following equations hold true:
在本实验中，我测量了图 6-10A和6-10B中所有串联电阻负载下电池两端的电压E = 6.30 V。然后，我将电压表连接到前两个串联电阻的两端。（图 6-10A显示了电阻的额定值，图 6-10B显示了我用欧姆表读取的值。）我按如下方式测量了电阻：
During this experiment, I measured E = 6.30 V across the battery when it operated under a load of all the series-connected resistors in Figs. 6-10A and B. Then I connected the voltmeter across the series combination of the first two resistors only. (Figure 6-10A shows the rated values of the resistors while Fig. 6-10B shows the values I read from my ohmmeter.) I measured the resistances as follows:
图 6-10 A 处为电阻分压器电压测量装置。此处，电压表连接至电阻器，用于测量第一电阻和第二电阻串联组合两端的电位差 E₂ 。所有电阻单位均为欧姆。实心点表示端子，虚线表示跳线。B 处为网络电流测量装置。A 处的电阻值为额定值，B 处的电阻值为实测值。
FIG. 6-10 At A, arrangement for measuring voltages in a resistive divider. Here, the voltmeter is connected to measure the potential difference E2 across the series combination of the first and second resistors. All resistances are in ohms. Solid dots indicate terminals. Dashed lines indicate jumpers. At B, arrangement for measuring current through the network. At A, the resistances are the rated values. At B, the resistances are my measured values.
R1 = 220欧姆
R1 = 220 ohms
R2 = 328欧姆
R2 = 328 ohms
R3 = 465欧姆
R3 = 465 ohms
R4 = 671欧姆
R4 = 671 ohms
将万用表设置为测量毫安 (mA) 电流。如图6-10B所示，通过万用表将电池连接到电阻网络，并测量电流。根据理论，我预期毫安表的读数应等于电池电压除以我测量的各电阻之和：
Set your meter to measure current in milliamperes (mA). Connect the battery to the resistive network through the meter as shown in Fig. 6-10B, and measure the current. According to strict theory, I expected the milliammeter to indicate a value equal to the battery voltage divided by the sum of my measured resistances:
当我测量电流时，我得到了 3.73 mA，这个值与理论值仅相差百分之一毫安 (0.01 mA)！
When I measured the current, I got 3.73 mA, a value only a hundredth of a milliampere (0.01 mA) different from the theoretical value!
现在，将万用表设置为中等直流电压量程，测量中间电压E1至E4 。黑色表笔应直接连接到电池负极并保持连接。红色表笔应依次连接到每个正电压点。首先测量电阻 R1 两端的电压E1。然后，按照图6-9的示意图（假设n = 4）所示顺序测量各电压：
Now measure the intermediate voltages E1 through E4 with your meter set for a moderate DC voltage range. The black meter probe should go directly to the negative battery terminal and stay there. The red meter probe should go to each positive voltage point in turn. First measure the voltage E1 that appears across R1 only. Then measure, in order, the voltages as illustrated in the schematic of Fig. 6-9 (assuming n = 4):
• R1 + R2两端的电势E2
• The potential E2 across R1 + R2
• R1 + R2 + R3之间的电势E3
• The potential E3 across R1 + R2 + R3
• R1 + R2 + R3 + R4两端的电势E4
• The potential E4 across R1 + R2 + R3 + R4
图 6-11 用于测试电阻分压器工作的电路。电池电压 E、第一电阻和第二电阻串联组合两端的电位差 E2 以及电阻值均为我的测量值。
FIG. 6-11 Circuit for testing the operation of a resistive voltage divider. The battery voltage E, the potential difference E2 across the series combination of the first and second resistors, and the resistances represent my measurements.
现在将万用表连接到R1 + R2组合电阻两端。如图 6-12所示，用跳线连接到面包板上其他位置的负载电阻两端。这样，电压源E2会使一部分电流流过负载电阻（我们称之为 R1L ），同时仍有一部分电流会继续流过 R1和R2 。尝试用你手头所有的电阻代替R1L 。如果你拥有零件清单中的所有电阻，你将需要进行七次测试，使用的电阻阻值范围从 220 欧姆到 3300 欧姆。
Now connect the meter across the combination R1 + R2. Run jumper wires to the ends of a load resistor located elsewhere on the breadboard, as shown in the layout diagram of Fig. 6-12. This arrangement will cause the voltage source E2 to drive some current through the load resistor (which we’ll call RL), in addition to some current that will keep flowing through R1 and R2. Try every resistor in your repertoire in the place of RL. If you obtained all the resistors in the parts list, you’ll have seven tests to do, using resistors rated at values ranging from 220 to 3300 ohms.
图 6-12用于测试负载下电阻分压器的电路。虚线表示跳线。该图显示了 当负载电阻RL交替连接到R1和 R2的串联组合和断开时，测量 E2 变化的装置。
FIG. 6-12 Circuit for testing a resistive voltage divider under load. Dashed lines indicate jumpers. This diagram shows the arrangement for measuring variations in E2 as the load resistance RL is alternately connected and disconnected from the series combination of R1 and R2.
或者，连接和断开分压器与 RL 之间的一根跳线，以便观察额外负载对E2的影响。你会发现，额外负载会影响分压器的工作特性。随着RL的减小，E2也随之减小。随着RL 的减小，这种影响变得更加显著，这代表着“负载越来越重”。表 6-2显示了我得到的结果。
Alternately, connect and disconnect one of the jumper wires between the voltage divider and RL, so you can observe the effect of the extra load on E2. As you’ll see, the additional load affects the behavior of the voltage divider. As RL decreases, so does E2. The effect grows more dramatic as RL decreases, representing a “heavier and heavier load.” Table 6-2 shows the results I got.
表 6-2 列出了我根据图 6-12构建的电阻分压器中，在不同负载上测得的电压值。文中已标明我测得的网络电阻分别为：R1 = 220 欧姆，R2 = 328 欧姆，R3 = 465 欧姆，R4 = 671 欧姆。我测得的负载电阻（左列）与网络电阻略有不同（因为它们涉及不同的物理元件！），其数值分别为 3300 欧姆、1500 欧姆、1000 欧姆、680 欧姆、470 欧姆、330 欧姆和 220 欧姆电阻的实际阻值，从上往下依次排列。
TABLE 6-2 Here are the voltages that I measured across various loads in a resistive voltage divider constructed according to Fig. 6-12. My measured network resistances, indicated in the text, were R1 = 220 ohms, R2 = 328 ohms, R3 = 465 ohms, and R4 = 671 ohms. My measured load resistances (left column), which differed a bit from the network resistances (because they involved different physical components!), were the actual values for resistors rated at 3300, 1500, 1000, 680, 470, 330, and 220 ohms, respectively as you read down.
将结果以点的形式绘制在坐标网格上，横轴为R<sub> L </sub>，纵轴为E <sub>2 </sub>。连接这些点，近似绘制一条特征曲线，该曲线表示E<sub> 2 </sub> 与R<sub> L </sub> 的关系。图 6-13是我绘制的图表。我使用了反对数坐标来表示R<sub> L</sub>，以便数值看起来更分散。该图清晰地展示了负载电导率增加时发生的情况。
Plot your results as points on a coordinate grid with RL on the horizontal axis and E2 on the vertical axis. Connect the dots to approximate a characteristic curve that shows E2 as a function of RL. Figure 6-13 is the graph I made. I used a reverse logarithmic scale to portray RL so the values would appear spread out. This graph provides a clear picture of what happens as the conductance of the load increases.
图 6-13电压分压器中输出电压与负载电阻 R <sub>L</sub>的关系测量结果。虚线表示 R<sub> 1</sub>和 R<sub> 2 </sub> 串联时的开路（空载）电压。空心圆圈表示不同负载下的测量电压。实线曲线显示了当 R <sub>L </sub> 减小时电路的响应情况。
FIG. 6-13 My measurements of output voltage vs. load resistance RL in the voltage divider. The dashed line shows the open-circuit (no-load) voltage across the combination of R1 and R2 in series. Open circles show the measured voltages across various loads. The solid curve lets you see how the circuit behaves as RL goes down.
基于二极管的降压器
A Diode-Based Voltage Reducer
整流二极管可以降低直流电源的输出电压，与电阻分压器相比，它能更精确地获得特定电压。让我们来搭建一个吧！本实验需要两个整流二极管。我使用的二极管额定电流为 1 A，峰值反向电压(PIV) 为 600 V，不过更高额定值的二极管也可以使用。此外，您还需要表 6-1中列出的每种电阻各一个，以及一些跳线。
Rectifier diodes can reduce the output voltage of a DC power source, providing a more predictable way to get specific voltages than a resistive divider can do. Let’s build one! For this experiment, you’ll need two rectifier diodes. Those that I obtained were rated at 1 A and 600 peak inverse volts (PIV), although higher ratings will work too. You’ll also need at least one of each resistor listed in Table 6-1, along with some jumpers.
图 6-14显示了整流二极管的原理图符号。制造商可以通过将一块P 型半导体材料与一块N 型半导体材料连接起来，形成所谓的PN 结来生产这种器件。图中用短直线表示的 N 型半导体构成阴极，用箭头表示的 P 型半导体构成阳极。在大多数情况下，电子可以很容易地从阴极流向阳极（逆箭头方向），但不能从阳极流向阴极（顺箭头方向）。通常或理论上的电流总是从正极流向负极，其方向与箭头所指的方向一致。
Figure 6-14 shows the schematic symbol for a rectifier diode. Manufacturers can produce one of these things by joining a piece of P-type semiconductor material to a piece of N-type material, creating a so-called P-N junction. The N-type semiconductor, represented by the short, straight line, forms the cathode. The P-type semiconductor, represented by the arrow, forms the anode. Under most conditions, electrons can move easily from the cathode to the anode (against the arrow), but not from the anode to the cathode (with the arrow). Conventional or theoretical current, which always goes from positive to negative, flows in the direction that the arrow points.
图 6-14 半导体二极管的示意图。线代表阴极，箭头代表阳极。
FIG. 6-14 Schematic symbol for a semiconductor diode. The line represents the cathode. The arrow represents the anode.
图 6-15 为电池、电阻器、电流表和二极管的串联连接。在 A 点，正向偏置允许电流通过，前提是电压等于或超过正向击穿阈值。在 B 点，反向偏置不会使电流流过二极管（除非电压非常高）。
FIG. 6-15 Series connection of a battery, resistor, current meter, and diode. At A, forward bias allows current to flow if the voltage equals or exceeds the forward breakover threshold. At B, reverse bias drives no current through the diode (unless the voltage gets very high).
要使电流流过正向偏置的二极管，需要一定的最小电压。工程师称这个阈值为正向击穿电压。大多数二极管的正向击穿电压只有几分之一伏，但会根据二极管的过载电流略有变化。如果PN结上的正向偏置电压不等于或超过正向击穿电压，二极管就不会导通。当二极管正向偏置并与电阻和电池串联时，PN结电压会下降到大约等于正向击穿电压的程度。与电阻的电压下降不同，二极管的压降能力几乎不会随着外部负载电阻的变化而变化。
It takes a certain minimum voltage to drive current through a forward-biased diode. Engineers call this threshold the forward breaker voltage. In most diodes it’s a fraction of a volt, but it varies somewhat depending on how much current you force the diode to carry. If the forward-bias voltage across the P-N junction does not equal or exceed the forward breaker voltage, then the diode won’t conduct. When you forward-bias a diode and connect it in series with a resistor and a battery, the P-N junction voltage goes down to an extent approximately equal to the forward breakover voltage. Unlike the voltage reduction that takes place with resistors, a diode’s voltage-dropping capability stays nearly constant as you vary the external load resistance.
虽然通常情况下电流不会流过反向偏置的二极管，但也有例外。如果反向电压足够高（通常远高于正向击穿电压），二极管会由于所谓的雪崩效应而导通。常用于直流电源稳压的齐纳二极管就是基于这一原理工作的。
Although current won’t normally flow through a reverse-biased diode, exceptions occur. If the reverse voltage gets high enough (usually much more than the forward breakover value), a diode will conduct because of so-called avalanche effect. Zener diodes, often used to regulate DC power-supply voltage, work according to this principle.
如图 6-16所示，您可以串联两个极性相同的二极管来搭建一个降压电路，这样，如果正向偏置电压足够高，电流就会流过负载电阻 R<sub> L</sub> 。图 6-17展示了如何在面包板上安装这些元件。将万用表设置为直流电压档位，量程在 0 到 20 V 之间。将万用表连接到负载电阻R<sub> L</sub>两端，注意极性，确保读数为正值。依次用不同的电阻代替 R<sub> L </sub>，并测量每次 R<sub> L </sub> 两端的电压。您需要进行七次测试，电阻值范围从 220 欧姆到 3300 欧姆。
You can set up a voltage reducer with two diodes in series and their polarities in agreement as shown in Fig. 6-16, so that current flows through the load resistor RL if the forward bias voltage is high enough. Figure 6-17 shows an arrangement for mounting the components on your breadboard. Set your meter to indicate DC voltage in a moderate range such as 0 to 20 V. Connect the meter across the load resistance RL, paying attention to the polarity so that you’ll get positive meter readings. Try each one of your resistors in the place of RL. Measure the voltage across RL in every case. You’ll have seven tests to do, with rated resistances ranging from 220 to 3300 ohms.
图 6-16 示意图显示了双二极管降压器中负载电阻上的电压测量。
FIG. 6-16 Schematic showing voltage measurement across the load resistance in a two-diode voltage reducer.
图 6-17为双二极管降压器中 测量负载电阻 R<sub> L</sub>两端电压的建议面包板布局。实心点表示面包板端子，虚线表示跳线。注意二极管极性！阴极应朝向电池负极。
FIG. 6-17 Suggested breadboard layout for measuring voltage across the load resistance RL in a two-diode voltage reducer. Solid dots show breadboard terminals. Dashed lines indicate jumpers. Pay attention to the diode polarities! The cathodes should face toward the negative battery terminal.
负载电阻R<sub> L</sub>会影响二极管降压器的性能，但其影响方式与电阻分压器不同。在进行这些测试时，你会发现，随着负载电阻R <sub>L</sub>的减小，负载两端的电位差也会下降，但下降幅度很小。随着R<sub> L</sub> 的减小，负载两端的电压下降速度越来越慢。与此形成对比的是电阻分压器，其电压会随着R <sub>L </sub>的减小而迅速下降。表 6-3显示了我使用这种双二极管电路测量不同R<sub> L</sub>值时得到的电压结果。
The load resistance RL affects the behavior of a diode-based voltage reducer, but in a different way than it affects the behavior of a resistive voltage divider. As you perform these tests, you’ll see that as the load resistance RL decreases, the potential difference across it goes down, but only a little. The voltage across the load tends to drop more and more slowly as RL decreases. Contrast this behavior with that of the resistive voltage divider, in which the voltage drops off more and more rapidly as RL decreases. Table 6-3 shows the results I got when I measured the voltages across various values of RL with this two-diode arrangement.
表 6-3 列出了我使用不同负载连接到二极管式降压器时获得的输出电压。这些是我测量的电阻值。（当然，您的测量结果会略有不同。）该电路包含两个额定电流为 1 A、峰值反向电压为 600 Ω 的二极管，它们正向偏置并与一个 6.30 V 的电池串联。
TABLE 6-3 Here are the output voltages that I obtained with various loads connected to a diode-based voltage reducer. These are the resistances that I measured. (Yours will of course differ a bit.) The circuit comprised two diodes rated at 1 A and 600 PIV, forward-biased and connected in series with a 6.30-V battery.
将你的结果以点的形式绘制在坐标系中，横轴为负载电阻R <sub>L </sub>，纵轴为R<sub> L </sub> 两端的电压，然后像上一个实验那样拟合曲线。我得到了图 6-18所示的曲线。和之前一样，我使用了反对数坐标来表示负载电阻。将此曲线与上一个实验的图 6-13进行比较。
Plot your results as points on a coordinate grid with the load resistance RL on the horizontal axis and the voltage across RL on the vertical axis, and then approximate the curve as you did in the previous experiment. I got the graph of Fig. 6-18. As before, I used a reverse logarithmic scale to portray the load resistance. Compare this graph with Fig. 6-13 from the previous experiment.
图 6-18为我测量的双二极管降压器输出电压与负载电阻 R<sub> L</sub>的关系曲线。虚线表示开路（空载）电压。空心圆圈表示不同负载下的测量电压。实线曲线显示了 R <sub>L</sub>减小时电路的响应特性。
FIG. 6-18 My measurements of output voltage vs. load resistance RL for the two-diode voltage reducer. The dashed line shows the open-circuit (no-load) voltage. Open circles show measured voltages across various loads. The solid curve reveals how the circuit behaves as RL goes down.
系列中不匹配的灯具
Mismatched Lamps in Series
当两个不同的白炽灯串联工作时，它们会接收到不同的电压，并消耗不同的伏安(VA) 功率，本实验将对此进行演示。（回想一下基础电学课程，在直流电路中，功率（瓦特）等于电压（伏特）乘以电流（安培），因此直流功率被称为伏安。）你需要一个 6.3V 的灯泡、一个 7.5V 的灯泡、一节四节 AA 电池以及一个设置为电压测量模式的万用表，如图6-19所示。你还需要一些跳线。
When two dissimilar incandescent lamps operate in series, they receive different voltages and consume different amounts of volt-ampere (VA) power, as this experiment demonstrates. (Remember from your basic electricity courses that in a DC circuit, power in watts equals voltage in volts times current in amperes, hence the term volt-ampere for simple DC power.) You’ll need a 6.3-V lamp, a 7.5-V lamp, a battery of four AA cells, and your multimeter set to measure voltage, as shown in the schematic of Fig. 6-19. You’ll also need some jumpers.
图 6-19 测量串联的两个不同灯泡中电压 E 1的较大值。
FIG. 6-19 Measurement of voltage E1 across the more negative of two dissimilar lamps in series.
你的面包板上应该有两个螺口灯座。将面包板放置成两个灯座并排位于顶部附近（图 6-20）。在左侧灯座中安装一个 6.3V 的灯泡，在右侧灯座中安装一个 7.5V 的灯泡。用一小段裸线牢固地连接端子 D1 和 D2，使左侧灯座的上端子连接到右侧灯座的下端子。然后用跳线连接灯座的空闲端子和电池端子，使两个灯泡串联工作。连接电池后，两个灯泡应该都会发出部分亮度的光。
Your breadboard should have two screw-base lamp holders. Position the board so that both holders lie near the top, side by side (Fig. 6-20). Install a 6.3-V lamp in the left-hand socket, and a 7.5-V lamp in the right-hand socket. Connect a short length of bare wire securely between terminals D1 and D2, so the top terminal of the left-hand lamp holder goes to the bottom terminal of the right-hand lamp holder. Then connect jumpers between the free lamp socket terminals and the battery terminals so the lamps operate in series. When you connect the battery to send current through the lamps, they both should glow at partial brilliance.
图 6-20 图 6-19 原理图的面包板布局。
FIG. 6-20 Breadboard layout for the schematic of Fig. 6-19.
将靠近电池负极的灯泡称为“灯泡 N”，它应该是左侧的灯泡。将靠近电池正极的灯泡称为“灯泡 P”，它应该是右侧的灯泡。拧下灯泡 N。当接触不良时，两个灯泡都会熄灭。重新拧上灯泡 N，然后拧下灯泡 P。两个灯泡再次熄灭。这演示了串联电路的工作原理：电路中任何一点的断路都会阻止电流在电路中流动。
Call the lamp closer to the negative battery terminal “lamp N.” That should be the one on the left. Call the lamp closer to the positive battery terminal “lamp P.” That should be the one on the right. Unscrew lamp N. When contact fails, both lamps will go dark. Screw lamp N back in, and then unscrew lamp P. Once again, both lamps will go dark. This demonstrates how a series circuit behaves: A break at any point prevents current from flowing anywhere in the circuit.
现在用跳线将灯泡 N（额定电压 6.3V）短接。由于灯泡 N 两端没有电压，它会熄灭，而灯泡 P（额定电压 7.5V）会几乎达到最大亮度。然后断开灯泡 N 上的跳线，并将跳线移到灯泡 P 上进行短接。灯泡 P 会熄灭，而灯泡 N 会以 100% 的亮度发光。这种现象再次体现了串联电路的典型特征。如果任何一个元件短路，其他所有元件都会消耗比之前更多的功率。
Now short out lamp N (the one rated at 6.3 V) with a jumper. It will go dark because it no longer has any voltage across it, while lamp P (rated at 7.5 V) will attain nearly full brilliance. Then disconnect the jumper from lamp N and move the jumper to short out lamp P instead. Lamp P will go dark while lamp N glows at 100 percent of full brilliance. Again, this behavior typifies series circuits. If any component shorts out, all the others consume more power than before.
将万用表设置为直流电压档。连接跳线，使灯泡串联，且两个灯泡均以部分亮度发光。测量灯泡 N 两端的电压E1 ，如图6-19和6-20所示。然后测量灯泡 P 两端的电压E2 ，如图 6-21的原理图和图 6-22的等效布局图所示。进行这些测试时，我得到的万用表读数如下：
Set your meter to read DC volts. Connect the jumpers so the lamps are in series and both glow at partial brilliance. Measure the voltage E1 across lamp N as shown in Figs. 6-19 and 6-20. Then measure the voltage E2 across lamp P as shown in the schematic of Fig. 6-21 and the equivalent layout pictorial of Fig. 6-22. When I performed these tests, I got the meter readings:
图 6-21 测量串联的两个不同灯泡中电压较高的灯泡两端的电压。
FIG. 6-21 Measurement of voltage across the more positive of two dissimilar lamps in series.
图 6-22 图 6-21原理图的面包板布局。
FIG. 6-22 Breadboard layout for the schematic of Fig. 6-21.
E1 = 2.20 V
E1 = 2.20 V
和：
and:
E2 = 3.64 V
E2 = 3.64 V
现在，请确定图 6-23原理图和图 6-24布局图中所示的串联灯泡两端的电压E。理论上，您的万用表应该显示各灯泡电压之和，即E = E₁ + E₂，这等于电池电压。当我将各个灯泡的测试结果代入此公式时，我预测会看到……
Now determine the voltage E across the series combination of lamps as shown in the schematic of Fig. 6-23 and the layout pictorial of Fig. 6-24. In theory, your meter should display the sum of the lamp voltages, or E = E1 + E2, which equals the battery voltage. When I input the results from my individual lamp tests into this formula, I predicted that I would see
图 6-23 测量两个不同灯泡串联组合两端的电压 E。
FIG. 6-23 Measurement of voltage E across the combination of two dissimilar lamps in series.
图 6-24 图 6-23原理图的面包板布局。
FIG. 6-24 Breadboard layout for the schematic of Fig. 6-23.
E = 2.20 + 3.64
E = 2.20 + 3.64
= 5.84 伏
= 5.84 V
我的万用表显示E = 5.85 V，接近灯泡两端电压之和，但明显低于空载条件下测得的 6.30 V 电池电压。显然，这些灯泡对四节电池的负载相当大。我也考虑过，在我的实验过程中，部分或全部 AA 电池可能已经老化。
My meter showed E = 5.85 V, close to the sum of the voltages across the lamps, but significantly lower than the 6.30 V battery voltage that I got under no-load conditions. Evidently, these bulbs load down the four-cell battery quite a lot. I also entertained the notion that some or all of the AA cells might have grown a little weak during the course of my experiments.
图 6-25 测量两个不同灯泡串联组合时所消耗的电流 I。
FIG. 6-25 Measurement of current I drawn by the combination of two dissimilar lamps in series.
图 6-26 图 6-25原理图的面包板布局。
FIG. 6-26 Breadboard layout for the schematic of Fig. 6-25.
现在您已经知道了每个灯泡两端的电压以及流过整个电路的电流，就可以分别计算每个灯泡以及它们共同消耗的伏安功率 (VA)。设P<sub> VA1 </sub> 表示灯泡 N 消耗的伏安功率，并使用以下公式：
Now that you know the voltage across each lamp and the current going through the whole circuit, you can determine VA power numbers for the lamps individually and together. Let PVA1 represent the VA power consumed by lamp N, and use the formula:
P VA1 = E 1 I
PVA1 = E1 I
我的结果如下：
My results came out as:
设P VA2表示灯 P 消耗的 VA 功率，则公式为：
Letting PVA2 represent the VA power consumed by lamp P, the formula is:
P VA2 = E 2 I
PVA2 = E2 I
在这种情况下，我得到了：
In this case, I got:
现在假设P VA表示两盏灯同时工作时消耗的伏安功率。在这种情况下，理论预测如下：
Now suppose that PVA represents the VA power consumed by both lamps operating together. In that case, theory predicts that:
P VA = EI
PVA = E I
当我输入实验结果时，我得到了
When I input my experimental results, I got
理论上，灯具组合消耗的伏安功率应该等于两个灯具单独消耗的伏安功率之和：
In theory, the VA power consumed by the lamp combination should also work out as the sum of the two VA power quantities taken individually:
P VA = P VA1 + P VA2
PVA = PVA1 + PVA2
将P VA1 = 0.306 和P VA2 = 0.506的结果相加，得到：
Adding my results of PVA1 = 0.306 and PVA2 = 0.506 gave me:
我的两个结果之间的误差只有百分之一的几分之一，这让我非常高兴！
The error between my two results was a small fraction of one percent, a state of affairs that made me happy indeed!
基于罗盘的电流计
A Compass-Based Galvanometer
在这个实验中，你将看到通电线圈如何影响磁罗盘的运行。电流产生磁场的现象称为电流效应。你需要一个以度为单位校准的露营或徒步旅行罗盘、1米长的漆包线、一张细砂纸、几个电阻（从你的收藏中挑选）、六节新的AA电池和一些跳线。你的面包板需要一个四节AA电池座和两个单节AA电池座。你还需要一个可以在薄纸板上打出6.4毫米（1/4英寸）孔的打孔器。
In this experiment, you’ll see how a current-carrying coil affects the behavior of a magnetic compass. The production of a magnetic field by an electric current is called galvanism. You’ll need a camper’s or hiker’s compass calibrated in degrees, 3 feet (1 meter) of enamel-coated magnet wire, a sheet of fine-grain sandpaper, several resistors from your collection, six fresh AA cells, and some jumpers. You’ll need your breadboard equipped with one holder for four AA cells and two holders for single AA cells. You’ll also need a “paper punch” that can put 1/4-inch (6.4-millimeter) holes in thin cardboard.
当把指南针靠近一根通有直流电的导线时，指南针的指针并不会精确地指向地磁北。相反，它的指针会向东或向西旋转。旋转的幅度取决于指南针与导线的距离以及导线中的电流大小。旋转的方向则取决于电流在导线中的流动方向以及导线放置在指南针的哪一侧。（导线应始终与指南针表面处于同一平面。）
When you place a compass near a wire that carries DC, the compass doesn’t point exactly toward geomagnetic north. Instead, its needle rotates to the east or west. The rotation extent depends on how close you bring the compass to the wire, and on how much current the wire carries. The rotation direction depends on which way the current flows through the wire and on which side of the compass you place the wire. (The wire should always lie in the same plane as the compass surface.)
将指南针水平放置，使指针指向刻度盘上的北方（地磁方位角0°），且线圈中电流为零时，如果附近没有磁性物体干扰指南针附近的地磁场，指针将指向地磁北。连接电池后，指南针指针会移动。随着连接更高电压的电池以增加电流，指南针指针的偏转角度也会增大，但无论向哪个方向旋转，都不会超过90°。反转施加电压的极性，指针的偏转方向也会反转。
When you place a compass on a horizontal surface so the needle points toward N on the scale (geomagnetic azimuth 0°) with zero current flowing in the coil, the needle will point toward geomagnetic north provided no nearby magnetic objects interfere with the geomagnetic field near the compass. When you connect a battery to the coil, the compass needle will move. As you connect higher-voltage batteries to increase the current, the compass needle deflection angle will increase, but it will never rotate more than 90° either way. Reversing the polarity of the applied voltage will reverse the direction of the needle deflection.
将 8-1/2 圈漆包铜线（不是裸铜线）绕在磁罗盘上，使线圈的匝数沿罗盘的 NS 轴排列，如图6-27所示。使用大多数五金店都能买到的细规格漆包线。为了确保线圈的机械稳定性，将指南针粘在一张长方形的薄纸板上，用打孔器在纸板上“N”字上方和“S”字下方打孔，然后将导线穿过这些孔，交替地从指南针上方和下方穿过。线圈两端各留出大约 10 厘米（4 英寸）的导线。
Wind 8-1/2 turns of enameled (not bare) copper wire around a magnetic compass so the coil turns lie along the N-S axis of the compass as shown in Fig. 6-27. Use small-gauge, enamel-coated wire of the sort available at most hardware stores. To ensure that you get a mechanically stable coil, glue the compass onto a rectangular sheet of thin cardboard, use the “paper punch” to put holes in the cardboard just above the N and just below the S, and then wind the wire through the holes, passing the wire alternately over and under the compass. Leave roughly 4 inches (10 centimeters) of wire to spare at each end of the coil.
图 6-27 电流计及其相关电路。指南针必须平放在水平面上。断开电池时，应将指南针放置成指针指向北方（地磁方位角 0°）。
FIG. 6-27 The galvanometer and associated circuitry. The compass must lie flat on a horizontal surface. Place it so the needle points toward N (geomagnetic azimuth 0°) when you disconnect the battery.
图 6-28 建议的电流计在面包板上的放置位置。连接电池正极的跳线通常应断开。切勿将此跳线连接到电池上超过几秒钟。图中，地磁北位于右侧。请注意电路板右下角的两个额外的单节电池支架。
FIG. 6-28 Suggested placement of the galvanometer on the breadboard. The jumper for the positive cell terminal should normally be disconnected. Never connect this jumper to the cell for more than a couple of seconds at a time. In this drawing, geomagnetic north lies off toward the right. Note the two additional single-cell holders in the lower right-hand part of the board.
用细砂纸打磨导线两端，去除 2.54 厘米（1 英寸）的漆包线。将圆规放在面包板上，把打磨过的导线末端分别缠绕在面包板的接线柱上。如果导线太长，打磨后修剪一下，使其刚好能整齐地位于线圈和面包板接线柱之间。图 6-28显示了我的布局。此图的方向为：面包板的右侧朝上。指向地磁北方向。调整电路板，使指南针指针指向刻度上的 N 点。确保线圈中没有电流。
Use a sheet of fine sandpaper to remove 1 inch (2.54 centimeters) of enamel from each end of the wire. Place the compass onto your breadboard, and wind each sanded-off end of the wire around one of the terminal nails. If the wires are too long, trim them so they’ll fit neatly between the coil and the breadboard terminals after you’ve sanded off the ends. Figure 6-28 shows my layout. This drawing is oriented so the right-hand side of the breadboard points toward geomagnetic north. Align the board so the compass needle points toward N on the scale. Make sure that the coil carries no current.
用一根跳线将线圈的一端连接到一节AA电池的负极。用另一根跳线连接到线圈的另一端。然后，将该跳线的“非线圈端”接触电池的正极几秒钟。指南针的指针应该顺时针或逆时针旋转近90°，使其指向地磁东偏北或地磁西偏北。不要让电流计直接连接到电池上超过几秒钟，因为线圈会在电池两端形成近乎完美的短路。
Use a jumper to connect one end of the coil to the negative terminal of a single AA cell. Connect another jumper to the other end of the coil. Then, for a couple of seconds, touch the “non-coil” end of that jumper to the positive cell terminal. The compass needle should rotate clockwise or counterclockwise by almost 90° so it points either slightly north of geomagnetic east or slightly north of geomagnetic west. Don’t leave the galvanometer connected directly to the cell for more than a couple of seconds at a time, because the coil creates an almost perfect short circuit across the cell.
取一个额定电阻为 680 欧姆的电阻、一个额定电阻为 470 欧姆的电阻、一个额定电阻为 330 欧姆的电阻，以及五个额定电阻为 220 欧姆的电阻。使用之前几个实验中用过的四节 AA 电池串联。用跳线将电池负极连接到检流计线圈的一端。在电路板上选择两个相邻的钉子作为电阻串联的位置。将一个 680 欧姆电阻的引线缠绕在这两个钉子上。钉子。用另一根跳线，将电阻的一端连接到电池正极。将数字万用表调到中等直流电流量程。我的万用表量程是 0 到 200 mA。这个量程对我来说很有效。
Take a resistor rated at 680 ohms, another rated at 470 ohms, another rated at 330 ohms, and five more rated at 220 ohms. Use the series combination of four AA cells from the past few experiments. With a jumper, connect the negative battery terminal to one end of the galvanometer coil. Choose two adjacent nails on the board as the location for the resistance to go in series with the galvanometer. Wrap the leads of a 680-ohm resistor around these nails. Using another jumper, connect one end of the resistor to the positive battery terminal. Switch your digital meter to a moderate DC current range. My meter has a setting for 0 to 200 mA. This worked well for me.
断开数字万用表，将 680 欧姆的电阻器更换为 470 欧姆的电阻器。重复电流与偏转角的关系实验。对 330 欧姆的电阻器和 220 欧姆的电阻器重复上述步骤。将所有数字万用表和检流计的读数记录在表格中。
Disconnect your digital meter and replace the 680-ohm resistor with one rated at 470 ohms. Repeat the current-vs.-deflection experiment. Do the same with the 330-ohm resistor, and then with the 220-ohm resistor. Keep track of all your digital meter and galvanometer readings in tabular form.
图 6-29 电流计测试装置。确保在无电流条件下，指南针指针精确指向刻度上的 N，并且当电流流过线圈时，指针向 N 的东侧偏转。
FIG. 6-29 Arrangement for testing the galvanometer. Make sure the compass needle points exactly toward N on the scale under no-current conditions, and deflects toward the east of N when current flows through the coil.
将第二个 220 欧姆的电阻与现有电阻并联，使阻值达到 110 欧姆。重复测量。在并联电路中再加入第三个 220 欧姆的电阻，使阻值约为 73 欧姆，并再次测试系统。然后并联第四个 220 欧姆的电阻，使阻值约为 55 欧姆；再次测试。最后并联第五个 220 欧姆的电阻，使阻值约为 44 欧姆，并再次测试。
Wrap a second 220-ohm resistor in parallel with the existing one so you get 110 ohms. Repeat the measurements. Add a third 220-ohm resistor to the parallel combination to get approximately 73 ohms, and test the system again. Then add a fourth 220-ohm resistor in parallel, getting about 55 ohms; test again. Then add a fifth 220-ohm resistor to get about 44 ohms, and test yet another time.
利用单节电池座提高电池电压。在每个电池座中放入一节新的AA电池。将其中一节新电池与原有的四节电池串联，得到一个五节电池组，并重复实验，电阻为44欧姆。然后，再串联一节新电池，得到一个六节电池组，并再次重复实验，电阻同样为44欧姆。
Increase the battery voltage by taking advantage of the single-cell holders. Place a fresh AA cell into each holder. Wire one of the new cells in series with the four existing cells to get a five-cell battery, and repeat the experiment with 44 ohms of resistance. Then wire another new cell in series to get a six-cell battery, and once again, do the experiment with 44 ohms of resistance.
完成所有测量并记录数字电流表和检流计的读数后，请编制一个表格，表格第一列（最左侧）填写AA电池数量，第二列填写电阻额定值，第三列填写电流值，第四列（最右侧）填写指南针指针偏转角度。表6-4显示了我的结果。你的结果无疑会与我的略有不同。
After you’ve made all the measurements and written down all the readings from your digital current meter and galvanometer, compile a table showing the number of AA cells in the first (leftmost) column, the rated resistor values in the second column, the current levels in the third column, and the compass needle deflection angles in the fourth (rightmost) column. Table 6-4 shows my results. Yours will doubtless differ somewhat from mine.
表 6-4 我用 AA 电池和电阻器与罗盘式电流计串联后得到的电流水平和偏转角。
TABLE 6-4 Current levels and deflection angles that I obtained with AA cells and resistors in series with a compass-based galvanometer.
图 6-30 直流电流计的指南针偏转与线圈电流的关系图。该图反映了我的实验结果，结果见表6-4。
FIG. 6-30 Compass needle deflection vs. coil current for the DC galvanometer. This graph reflects my experimental results, which appear in Table 6-4.
总结与结论
Summary and Conclusion
当你想设计、制造、调试和排除电子设备故障时，最好能有一份好的电路图（或一套电路图）作为参考。图示，包括布局图，会有所帮助。但是，当你真正进入实验室进行实际操作时，你会发现没有什么能替代真实的硬件。
When you want to design, build, debug, and troubleshoot electronic equipment, you’ll do best if you have a good schematic (or set of schematics) to work with. Pictorial diagrams, including layouts, can help. But when you get in your lab and do the physical work, you’ll never find any substitute for real-world hardware.
如果你完成了本章的所有实验，你的结果几乎肯定会与我的略有不同。例如，如果你在最后一个实验中替换了主要部件（比如灯泡），那么你的某些结果可能与我的大相径庭。无论你是亲自动手做了实验，还是仅仅凭想象进行推导，你都有机会了解原理图、示意图、图表和表格是如何协同工作的。所有这些工具都应是工程师知识库中不可或缺的一部分。
If you did all the experiments in this chapter, you almost certainly came up with results a little different from mine. If you had to make major parts substitutions, for example, with the lamps in the last experiment, then some of your results came out a lot different than mine. Whether you performed the experiments or merely followed along in your imagination, you got a chance to see how schematics, pictorials, graphs, and tables can work together. All these tools belong in an engineer’s knowledge base.
再次，请允许我“厚颜无耻地”推销一下我的书《在家就能做的电学实验》。这本书能让你获得一些动手实践的实验经验，还能学到一些理论知识。你还会看到一些相当奇特的现象！如果你想要更全面地了解电学和电子学，以及大量的电路图和足以让真正的技术宅都乐在其中的数学知识，我推荐我的书《自学电学和电子学》的最新版。这两本书都由麦格劳-希尔出版社出版，你可以在各大在线零售商处找到它们。你甚至可能在传统的实体书店或当地的公共图书馆/学校图书馆里找到它们！
Again, please let me make a “shameless plug” for my book Electricity Experiments You Can Do at Home. You’ll get some hands-on lab experience and a bit of theory from that book. You’ll also see some rather strange phenomena! If you want a more exhaustive presentation of electricity and electronics along with plenty of schematics and enough mathematics to keep a true nerd from getting bored, I recommend the latest edition of my book Teach Yourself Electricity and Electronics. Both books are published by McGraw-Hill, and you can find them at major online retailers. You might even come across them at an old-style “bricks and mortar” book store or your local public or school library!
一个
A
原理图符号
Schematic Symbols
B
B
电阻色码
Resistor Color Codes
大多数电阻器都有彩色环带或区域来指示其阻值和容差。大多数碳膜电阻器和薄膜电阻器周围都有三、四或五条环带。其他一些电阻器体积较大，可以直接印上数字来表示其阻值和容差。
Most resistors have colored bands or regions that indicate their values and tolerances. You’ll see three, four, or five bands around most carbon-composition resistors and film resistors. Other resistors have enough physical bulk to allow for printed numbers that tell you the values and tolerances directly.
对于轴向引线（导线从两端笔直引出）的电阻器，第一、二、三、四、五色环的排列方式如图B-1所示。对于径向引线（导线从两端垂直于元件轴线引出）的电阻器，色环的排列方式如图B-2所示。前两个色环代表 0 到 9 的个位数，第三个色环代表 10 的某个幂次方。（暂时忽略第四和第五色环。）表 B-1列出了各种颜色对应的数字。
On resistors with axial leads (wires that come straight out of both ends), the first, second, third, fourth, and fifth bands are arranged as shown in Fig. B-1. On resistors with radial leads (wires that come off the ends at right angles to the axis of the component body), the colored regions are arranged as shown in Fig. B-2. The first two regions represent single digits 0 through 9, and the third region represents a multiplier of 10 to some power. (For the moment, don’t worry about the fourth and fifth regions.) Table B-1 indicates the numerals corresponding to various colors.
图 B-1 轴向引线电阻器上色环的位置。
FIG. B-1 Locations of color-code bands on a resistor with axial leads.
假设你找到一个电阻器，它有三条色环：黄色、紫色和红色，顺序依次为黄色、紫色和红色。你可以参考下表，从左到右读取以下信息：
Suppose that you find a resistor with three bands: yellow, violet, and red, in that order. You can read as follows, from left to right, referring to the table:
• 黄色 = 4
• Yellow = 4
• 紫色 = 7
• Violet = 7
• 红色 = ×100
• Red = ×100
你得出结论，额定电阻等于 4700 欧姆，即 4.7 千欧姆。
You conclude that the rated resistance equals 4700 ohms, or 4.7 k.
再举一个例子，假设你找到一个电阻器，其电阻器上有蓝色、灰色和橙色的色环。你查阅表 B-1并确定：
As another example, suppose you find a resistor with bands of blue, gray, and orange. You refer to Table B-1 and determine that:
表 B-1 列出 了大多数固定电阻器上出现的前三个色环或区域的色码。有关第四和第五个色环或区域的讨论，请参见正文。
TABLE B-1 Color codes for the first three bands or regions that appear on most fixed resistors. See text for discussion of the fourth and fifth bands or regions.
• 蓝色 = 6
• Blue = 6
• 灰度值 = 8
• Gray = 8
• 橙色 = ×1000
• Orange = ×1000
该序列告诉你，该电阻器的额定值为 68,000 欧姆，或 68 k。
This sequence tells you that the resistor is rated at 68,000 ohms, or 68 k.
如果电阻器表面有第四条色环（如图 B-1或B-2所示的 #4 ），则该标记表示电阻器的容差。银色色环表示 ±10%，金色色环表示 ±5%。如果没有第四条色环，则容差为 ±20%。
If a resistor has a fourth colored band on its surface (#4 as shown in Figs. B-1 or B-2), then that mark tells you the tolerance. A silver band indicates ±10%. A gold band indicates ±5%. If no fourth band exists, then the tolerance is ±20%.
图 B-2 径向引线电阻器上色标的位置。
FIG. B-2 Locations of color code designators on a resistor with radial leads.
第五条色环（如有）表示电阻在使用1000小时后，其电阻值可能出现的最大变化百分比。棕色色环表示最大变化为额定值的±1%。红色色环表示±0.1%。橙色色环表示±0.01%。黄色色环表示±0.001%。如果电阻器没有第五条色环，则表示在使用1000小时后，电阻值的偏差可能超过额定值的±1%。
The fifth band, if any, indicates the maximum percentage by which you should expect the resistance to change after the first 1000 hours of use. A brown band indicates a maximum change of ±1% of the rated value. A red band indicates ±0.1%. An orange band indicates ±0.01%. A yellow band indicates ±0.001%. If the resistor lacks a fifth band, it tells you that the resistor might deviate by more than ±1% of the rated value after the first 1000 hours of use.
合格的工程师或技术人员在将电阻器安装到电路中之前，总会用欧姆表测试其阻值。如果发现元件有缺陷或标签错误，遵循这一预防措施可以避免日后出现问题。检查电阻器的阻值只需几秒钟。如果您跳过这个简单的步骤，直接搭建电路，然后发现由于某个电阻器的问题导致电路无法工作，那么您可能需要花费数小时来查找问题所在！
A competent engineer or technician always tests a resistor with an ohmmeter before installing it in a circuit. If the component turns out defective or mislabeled, you can prevent potential future troubles by following this precaution. It takes only a few seconds to check a resistor’s ohmic value. If you skip that simple step, built a circuit, and then discover that it won’t work because of some miscreant resistor, you might have to spend hours tracking it down!
C
C
零件供应商
Parts Suppliers
全电子
All-Electronics
(800) 826-5432
(800) 826-5432
设计说明
Design Notes
（800）957-6867
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Electronix Express
(800) 972-2225
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(800) 831-4242
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建议延伸阅读
Suggested Additional Reading
Frenzel, Louis E., Jr.，《电子学原理》。Newnes/Elsevier，2010 年。
Frenzel, Louis E., Jr., Electronics Explained. Newnes/Elsevier, 2010.
Gerrish, Howard，《电力和电子学》。Goodheart-Wilcox 公司，2008 年。
Gerrish, Howard, Electricity and Electronics. Goodheart-Wilcox Co., 2008.
斯坦·吉比利斯科，《电力揭秘》，第二版。麦格劳-希尔，2011。
Gibilisco, Stan, Electricity Demystified, 2nd ed. McGraw-Hill, 2011.
斯坦·吉比利斯科，《电子揭秘》，第二版。麦格劳-希尔，2011。
Gibilisco, Stan, Electronics Demystified, 2nd ed. McGraw-Hill, 2011.
Gibilisco, Stan，《电子爱好者的业余无线电和短波无线电》。麦格劳-希尔出版社，2014 年。
Gibilisco, Stan, Ham and Shortwave Radio for the Electronics Hobbyist. McGraw-Hill, 2014.
Gibilisco, Stan，《自学电学和电子学》，第 6 版。McGraw-Hill，2016 年。
Gibilisco, Stan, Teach Yourself Electricity and Electronics, 6th ed. McGraw-Hill, 2016.
Kybett, Harry 和 Boysen, Earl，《完整的电子学自学指南及项目》，第 4 版，Wiley，2012 年。
Kybett, Harry and Boysen, Earl, Complete Electronics Self-Teaching Guide with Projects, 4th Ed. Wiley, 2012.
Monk, Simon，《电子技术破解》。麦格劳-希尔出版社，2013 年。
Monk, Simon, Hacking Electronics. McGraw-Hill, 2013.
Santiago, John，《电路分析入门》。For Dummies出版社，2013年。
Santiago, John, Circuit Analysis for Dummies. For Dummies, 2013.
Schertz, Paul 和 Monk, Simon，《发明家实用电子学》，第 3 版。McGraw-Hill，2013 年。
Schertz, Paul and Monk, Simon, Practical Electronics for Inventors, 3rd ed. McGraw-Hill, 2013.
指数
Index
请注意，索引链接指向的是纸质版的起始页码。在电子阅读器中，链接位置仅供参考，您可能需要在点击链接后向下翻页一次或多次才能找到索引内容。
Please note that index links point to page beginnings from the print edition. Locations are approximate in e-readers, and you may need to page down one or more times after clicking a link to get to the indexed material.
文中引用的数字用斜体字表示。
References to figures are in italics.
交流电。参见交流电（AC）。
AC. See alternating current (AC)
主动过滤器，130-131
active filters, 130–131
空气可变电容器，37
air variable capacitors, 37
空芯电感器，39-40
air-core inductors, 39–40
鳄鱼夹，143
alligator clips, 143
alternating current (AC), 15, 16
AM发射机，17
AM transmitters, 17
框图，20
block diagram, 20
安培，单位为144
amperes, as units, 144
调幅（AM）语音发射机。参见调幅发射机。
amplitude-modulated (AM) voice transmitters. See AM transmitters
与门，63-64
AND gates, 63–64
电枢，47
armatures, 47
音频频率（AF），103
audio-frequency (AF), 103
音频频率（AF）振荡器，8
audio-frequency (AF) oscillators, 8
雪崩效应，159
avalanche effect, 159
雪崩电压，52
avalanche voltage, 52
轴向引线，195
axial leads, 195
带通滤波器，120
bandpass filters, 120
电池，62-63
batteries, 62–63
泄放电阻，75-76
bleeder resistors, 75–76
出血，75
bleeds, 75
框图
block diagrams
AM 无线电发射机示意图，20
AM radio transmitter diagram, 20
电流和信号路径，18-20
current and signal paths, 18–20
流程图，20-24
flowcharts, 20–24
功能图，16-18
functional drawings, 16–18
用箭头连接的线条，15
interconnecting lines with arrows, 15
电源图，19
power supply diagram, 19
工艺路径，24-27
process paths, 24–27
体电容，37
body capacitance, 37
面包板，138-141
breadboard, 138–141
基于罗盘的电流计布局，172
layout for compass-based galvanometer, 172
电力实验布局，141
layout for electricity experiments, 141
双二极管降压器电压测量布局图，161
layout for measuring voltage in two-diode voltage reducer, 161
串联不匹配灯具的布局，164、165、167、168
layout for mismatched lamps in series, 164, 165, 167, 168
缓冲电路，89-90
buffer circuits, 89–90
电缆，50-52
cables, 50–52
校准图，175
calibration graph, 175
电容，133
capacitance, 133
身体，37
body, 37
外部，37
external, 37
碳膜电阻器，30
carbon-composition resistors, 30
另请参阅电阻器。
See also resistors
级联电路，107
cascading circuits, 107
猫的胡须，102
cat’s whiskers, 102
细胞，62-63
cells, 62–63
另见电化学电池
See also electrochemical cells
中心导体，50
center conductors, 50
频道，55
channels, 55
特征曲线，156
characteristic curves, 156
芯片。参见集成电路（IC）。
chips. See integrated circuits (ICs)
圆圈，6-7
circles, 6–7
电路图，67-76
circuit diagrams, 67–76
夹线，143
clip leads, 143
闭环配置，56
closed-loop configuration, 56
代码练习振荡器， 114、116、117、118
code practice oscillator, 114, 116, 117, 118
色码、电阻器、195-197
color codes, resistors, 195–197
原理图中的颜色，12
color in schematic diagrams, 12
基于罗盘的电流计，170-175
compass-based galvanometer, 170–175
元件公差，86-87
component tolerance, 86–87
成分
components
互连，7-9
interconnections, 7–9
标签，76-82，87-89
列表，139-140
list, 139–140
哪里可以买到，138
where to buy, 138
导体，48 –52
conductors, 48–52
传统电流，68
conventional current, 68
交叉电线，49-50
crossing wires, 49–50
晶体收音机，102-105
crystal radio receivers, 102–105
当前值，作为变量，144
current, as a variable, 144
截止频率，120，131-133
cutoff frequencies, 120, 131–133
直流电。参见直流电（DC）。
DC. See direct current (DC)
直流电源，74-76
DC power supplies, 74–76
解调器，102
demodulators, 102
探测器，102
detectors, 102
二极管真空管，59
diode vacuum tubes, 59
基于二极管的降压器，157-162
diode-based voltage reducers, 157–162
二极管，52-53
diodes, 52–53
directly heated cathodes, 60, 61
double-pole/double-throw (DPDT) switches, 44, 45
double-pole/single-throw (DPST) switches, 44, 45
106号公路
drive, 106
双二极管管，60
dual diode tubes, 60
双五极管，60
dual pentode tubes, 60
双四极管，60
dual tetrode tubes, 60
双管，60
dual tubes, 60
泥土地面，50
earth ground, 50
有效电压，76
effective voltage, 76
电气值标称，88-89
electrical value designations, 88–89
电化学电池，62-63
electrochemical batteries, 62–63
electrochemical cells, 62–63, 69
电磁铁，47
electromagnets, 47
电子管，58-62
electron tubes, 58–62
增强型 MOSFET，55
enhancement-mode MOSFET, 55
专属 OR 门，64
exclusive OR gates, 64
异或运算，64
exclusive-OR operations, 64
外部电容，37
external capacitance, 37
法拉第，35
farads, 35
另见电容器
See also capacitors
反馈，负面，56
feedback, negative, 56
场效应晶体管，54-55
field-effect transistors, 54–55
另请参阅电阻器。
See also resistors
滤波电容器，75
filter capacitors, 75
五极两掷 (5P2T) 开关，44 –45
five-pole/two-throw (5P2T) switches, 44–45
固定值电容器，35-36
fixed-value capacitors, 35–36
固定阻值电阻器，30
fixed-value resistors, 30
另请参阅电阻器。
See also resistors
闪光频率，17-18
flash rate, 17–18
手电筒电路，68-72
flashlight circuits, 68–72
流程图，20-24
flowcharts, 20–24
过程方向，24
direction of processes in, 24
工艺路径，24-27
process paths, 24–27
正向断路器电压，158
forward breaker voltage, 158
正向击穿电压，52
forward breakover voltage, 52
频率，17
frequency, 17
对比收益，57
vs. gain, 57
功能图，16-18
functional drawings, 16–18
增益与频率的关系，57
gain, vs. frequency, 57
方铅矿，102
galena, 102
电流刺激，170
galvanism, 170
电流计，罗盘式，170 –175
galvanometer, compass-based, 170–175
并联电容器，37-38
ganged capacitors, 37–38
联动开关，45-46
ganged switches, 45–46
大门，53
gates, 53
地理极点，170
geographic poles, 170
地磁极，170
geomagnetic poles, 170
网格偏差，92
grid bias, 92
接地阴极电路，94
grounded-cathode circuits, 94
接地网电路，94
grounded-grid circuits, 94
耿氏二极管，53
Gunn diodes, 53
另请参阅开关
See also switches
硬连接，9
hard wiring, 9
亨利（H），39
henrys (H), 39
另见电感
See also inductance
七节管，61-62
heptode tubes, 61–62
赫兹（Hz），17
hertz (Hz), 17
六角管，61-62
hexode tubes, 61–62
高状态，63
high state, 63
高通滤波器，120
highpass filters, 120
高通响应，57，131，132
highpass response, 57, 131, 132
混合图纸，89-91
hybrid drawings, 89–91
赫兹，17
Hz, 17
理想二极管，52
ideal diodes, 52
阻抗，94
impedance, 94
白炽灯，串联时型号不匹配，163-169
incandescent lamps, mismatched in series, 163–169
包容性运筹学操作，63
inclusive-OR operations, 63
indirectly heated cathodes, 59, 60, 61
电感，38-43
inductance, 38–43
电感器，38-43
inductors, 38–43
行业标准零件编号，88-89
industry standard part designations, 88–89
integrated circuits (ICs), 56, 102
反相宽带放大器，128-129
inverting broadband amplifiers, 128–129
inverting differentiators, 129, 130
输入反转，56
inverting inputs, 56
inverting integrators, 130, 131
铁芯电感器，41-42
iron-core inductors, 41–42
跳线，143
jumper wires, 143
结型场效应晶体管（JFET），54
junction field-effect transistors (JFET), 54
基尔霍夫，古斯塔夫·罗伯特，144-145
Kirchhoff, Gustav Robert, 144–145
基尔霍夫定律，143-147
Kirchhoff’s current law, 143–147
基尔霍夫第一定律。参见基尔霍夫当前定律。
Kirchhoff’s first law. See Kirchhoff’s current law
基尔霍夫第二定律。参见基尔霍夫电压定律
Kirchhoff’s second law. See Kirchhoff’s voltage law
基尔霍夫电压定律，147-150
Kirchhoff’s voltage law, 147–150
L 网络，112
L networks, 112
叠片铁芯电感器，41-42
laminated-iron core inductors, 41–42
语言、视觉、示意图，如9 – 13
language, visual, schematics as, 9–13
大型原理图，逐渐熟悉，122-127
large schematics, getting comfortable with, 122–127
布局图。参见图示。
layout diagrams. See pictorial diagrams
LC电路，111，117-120
铅，30
leads, 30
轴向，195
axial, 195
轻载，78
light load, 78
load resistance, 155–158, 160–162
逻辑电路，94-99
logic circuits, 94–99
逻辑门，63-64
logic gates, 63–64
及其特征，65
and their characteristics, 65
损失，42
loss, 42
低状态，63
low state, 63
低通滤波器，120
lowpass filters, 120
金属氧化物半导体场效应晶体管（MOSFET），54-55
metal-oxide-semiconductor field-effect transistors (MOSFET), 54–55
微法拉，35
microfarads, 35
另见电容器
See also capacitors
微亨利（μH），39
microhenrys (μH), 39
另见电感
See also inductance
毫亨利 (mH)，39
millihenrys (mH), 39
另见电感
See also inductance
混合, 61
mixing, 61
另请参阅开关
See also switches
多触点开关，45
multi-contact switches, 45
万用表，85-86
multimeters, 85–86
与非门，64
NAND gates, 64
纳米亨利（nH），39
nanohenrys (nH), 39
另见电感
See also inductance
N沟道耗尽型MOSFET ，54-55
N-channel depletion-mode MOSFET, 54–55
N沟道增强型MOSFET，55
N-channel enhancement-mode MOSFET, 55
N沟道结型场效应晶体管，54
N-channel junction field-effect transistors, 54
与三极管相比，93
vs. triode tubes, 93
非反相宽带放大器，128
non-inverting broadband amplifiers, 128
同相输入，56
non-inverting inputs, 56
无极性电容器，35-36
nonpolarized capacitors, 35–36
另见电容器
See also capacitors
常闭继电器，47
normally closed relays, 47
常开继电器，47
normally open relays, 47
非门，63-64，96-97
非门，64
NOT-AND gates, 64
N型半导体，158
N-type semiconductors, 158
欧姆，29
ohms, 29
以单位计，144
as units, 144
另请参阅电阻器。
See also resistors
欧姆定律，151
Ohm’s law, 151
one-pole/ten-throw (1P10T) switches, 45, 46
运算放大器，56-57
op amps, 56–57
电路，128-135
circuits, 128–135
开环配置，57
open-loop configuration, 57
运算放大器。参见运放。
operational amplifiers. See op amps
振荡器电路，90
oscillator circuits, 90
垫片电容器，36
padder capacitors, 36
分页符，109-111
page breaks, 109–111
零部件供应商，199
parts suppliers, 199
P沟道耗尽型MOSFET，54-55
P-channel depletion-mode MOSFET, 54–55
P沟道增强型MOSFET，55
P-channel enhancement-mode MOSFET, 55
P沟道结型场效应晶体管，54
P-channel junction field-effect transistors, 54
峰值反向电压 (PIV)，157
peak inverse volts (PIV), 157
峰值电压，76
peak voltage, 76
五极电网变换器，61
pentagrid converters, 61
相位反转，115
phase inversion, 115
相位相反，56
phase opposition, 56
皮法拉，35
picofarads, 35
另见电容器
See also capacitors
与示意图相比，13
vs. schematic diagrams, 13
π-L网络，113
pi-L networks, 113
捏住，55
pinchoff, 55
音调，115
pitch, 115
板。参见阳极。
plates. See anodes
PN 连接点，158
P-N junctions, 158
PNP双极晶体管符号，7-8
PNP bipolar transistor symbol, 7–8
极性，63
polarity, 63
极化电容器，35-36
polarized capacitors, 35–36
另见电容器
See also capacitors
杆，44
poles, 44
positive-ground system, 115, 116
不同的负面反馈，129
varying negative feedback, 129
雨刮器/滑块，111
wipers/sliders, 111
粉末铁芯电感器，42-43
powdered-iron core inductors, 42–43
电源
power supplies
DC ，74-76，115，116
倍压器，80
voltage-doubler, 80
前置放大器，103-104
preamplifiers, 103–104
电流守恒原理。参见基尔霍夫电流定律
principle of current conservation. See Kirchhoff’s current law
电压守恒原理。参见基尔霍夫电压定律
principle of voltage conservation. See Kirchhoff’s voltage law
工艺路径，24-27
process paths, 24–27
程序流程图，20-24
program flowcharts, 20–24
原型，68
prototypes, 68
P型半导体，158
P-type semiconductors, 158
穿孔卡片，24-26
punch cards, 24–26
另请参阅直流电 (DC)
See also direct current (DC)
推挽放大器，105-106
push-pull amplifiers, 105–106
收音机接收器，107-109，110
射频（RF）放大器，8
radio-frequency (RF) amplifiers, 8
整流器，17-18
rectifiers, 17–18
全波桥式整流器，78
full-wave bridge rectifiers, 78
继电器，47
relays, 47
电阻，133
resistance, 133
电阻，作为一个变量，144
resistance, as a variable, 144
电阻-电容（RC）组合，57
resistance-capacitance (RC) combination, 57
电阻分压器，150-157
resistive voltage dividers, 150–157
颜色代码，195 – 197
color codes, 195–197
共振，94
resonance, 94
共振频率，103
resonant frequency, 103
resonant notch, 57, 131, 134–135
共振峰，57、131、133-134
resonant peak, 57, 131, 133–134
响应曲线，57
response curves, 57
反向偏置，52，158，159
reverse logarithmic scale, 156, 160
射频场强计，72-74
RF field-strength meters, 72–74
变阻器，31-32
rheostats, 31–32
另见电位计
See also potentiometers
涟漪，75
ripple, 75
均方根值（RMS），76
root-mean-square (RMS), 76
转子，37
rotors, 37
原理图
schematic diagrams
颜色，12
color in, 12
发现故障部件，2
finding faulty component in, 2
与图示相比，13
vs. pictorial diagrams, 13
符号学，5-7
symbology, 5–7
作为一种视觉语言，9-13
as a visual language, 9–13
示意图/框图混合图，89-91页
schematic/block hybrid drawings, 89–91
屏幕网格，60
screen grids, 60
半导体二极管，52
semiconductor diodes, 52
硅控整流器（SCR），53
silicon-controlled rectifiers (SCR), 53
单刀双掷 (SPDT) 开关，44
single-pole/double-throw (SPDT) switches, 44
杠杆，47
levers, 47
single-pole/single-throw (SPST) switches, 44, 46
继电器，47
relays, 47
正弦波，130
sinusoid, 130
软件、流程图、20-24
software, flowcharts, 20–24
实心铁芯电感器，41-42
solid-iron core inductors, 41–42
杂散排放，93
spurious emissions, 93
定子，37
stators, 37
降压变压器，44
step-down transformers, 44
升压变压器，44
step-up transformers, 44
另请参阅开关
See also switches
频闪灯电路，18、126、127
strobe light circuit, 18, 126, 127
供应商、零件、199
suppliers, parts, 199
抑制栅格，60
suppressor grids, 60
开关，44-47
switches, 44–47
符号，177-194
symbols, 177–194
1P10T 交换机，46
1P10T switches, 46
5P2T 开关，45
5P2T switches, 45
空心变压器，43
air-core transformers, 43
箭头指向，32
arrows in, 32
同轴电缆，51
coaxial cables, 51
conductors that cross paths, 49, 50
二极管真空管，59
diode vacuum tubes, 59
双刀双掷开关，45
DPDT switches, 45
双刀单掷开关，45
DPST switches, 45
电导体，69
electrical conductors, 69
电化学电池，62
electrochemical batteries, 62
电子管元件，58
electron tube elements, 58
场强计组件，73
field-strength meter components, 73
固定电容器，35
fixed capacitors, 35
固定阻值电阻器，30
fixed-value resistors, 30
手电筒组件，72
flashlight components, 72
在流程图中，22-23
in flowcharts, 22–23
联动旋转开关，46
ganged rotary switches, 46
耿氏二极管，53
Gunn diodes, 53
白炽灯泡，69
incandescent bulbs, 69
集成电路（IC），56
integrated circuits (ICs), 56
79的字母缩写
letter abbreviations for, 79
莫尔斯电码键，47
Morse code keys, 47
N沟道耗尽型MOSFET，54
N-channel depletion-mode MOSFET, 54
N沟道增强型MOSFET，55
N-channel enhancement-mode MOSFET, 55
N沟道JFET，54
N-channel JFET, 54
NPN双极型晶体管，54
NPN bipolar transistors, 54
运算放大器，56
op amps, 56
P沟道耗尽型MOSFET，54
P-channel depletion-mode MOSFET, 54
P沟道增强型MOSFET，55
P-channel enhancement-mode MOSFET, 55
P沟道JFET，54
P-channel JFET, 54
PNP bipolar transistors, 7, 54
极化电容器，36
polarized capacitors, 36
powdered-iron core inductors, 42, 43
变阻器，32
rheostats, 32
旋转电位器，33
rotary potentiometers, 33
旋转，30
rotating, 30
在示意图中，5-7
in schematics, 5–7
半导体二极管，52
semiconductor diodes, 52
硅控整流器（SCR），53
silicon-controlled rectifiers (SCR), 53
solid- or laminated-iron core inductors, 41, 42, 43
实心或叠片铁芯变压器，43
solid- or laminated-iron core transformers, 43
SPDT继电器，48
SPDT relays, 48
单刀双掷开关，44
SPDT switches, 44
单刀单掷开关，44
SPST switches, 44
三端滚轮电感器，41
three-terminal roller inductors, 41
三端可变电阻器，32
three-terminal variable resistors, 32
三极真空管，59
triode vacuum tubes, 59
双芯电缆，52
two-conductor cable, 52
双端可变电阻器，31
two-terminal variable resistors, 31
变容二极管，53
varactor diodes, 53
可变空芯电感器，40
variable air-core inductors, 40
齐纳二极管，53
Zener diodes, 53
储能回路，94
tank circuits, 94
测试点（TP），86
test points (TPs), 86
四极真空管，60
tetrode vacuum tubes, 60
理论电流，68
theoretical current, 68
投掷次数，44
throws, 44
计时器，17-18
timers, 17–18
收发器，46-47
transceivers, 46–47
变压器，43-44
transformers, 43–44
晶体管，53-55
transistors, 53–55
微调电容器，36
trimmer capacitors, 36
三极真空管，59-60
triode vacuum tubes, 59–60
与 N 沟道结型场效应晶体管相比，93
vs. N-channel junction field-effect transistors, 93
故障排除
troubleshooting
到组件级别，121
to the component level, 121
附原理图，82-89
with schematics, 82–89
管，58-62
tubes, 58–62
twin-T oscillator, 115, 116, 118
非屏蔽电缆，50
unshielded cables, 50
真空管射频放大器，91-94
vacuum-tube RF amplifiers, 91–94
变容二极管，53
varactor diodes, 53
可变电容器，36-38
variable capacitors, 36–38
可变电阻器，31-34
variable resistors, 31–34
Vcc connection symbol, 56, 130
Vee connection symbol, 56, 130
电压，17
voltage, 17
作为变量，144
as a variable, 144
二极管式降压器，157-162
voltage reducers, diode-based, 157–162
电压调节器，19
voltage regulators, 19
倍压电源，80
voltage-doubler power supplies, 80
伏安 (VA)，163
volt-ampere (VA), 163
伏欧毫安表（VOM），85-86
volt-ohm-milliammeters (VOMs), 85–86
伏特，单位为144
volts, as units, 144
楔形X ，110，118，127
另见箭头
See also arrows
楔形Y ，118，119，127
另见箭头
See also arrows
楔形 Z，127
wedge Z, 127
另见箭头
See also arrows
绕线，142-143
wire wrapping, 142–143
线绕电阻器，30、31、33、34
wirewound resistors, 30, 31, 33, 34
另请参阅电阻器。
See also resistors
接线图，18
wiring diagrams, 18
另请参阅功能图
See also functional drawings
工作台，138
workbench, 138